diff --git a/main.yml b/main.yml
index 6cbfaa1..2fce9ef 100644
--- a/main.yml
+++ b/main.yml
@@ -49,7 +49,8 @@
       tags: [foundational, package-and-build, bespoke-pkg, mac-ports]
       vars:
         # https://www.macports.org/install.php
-        macports_version: "2.6.4_1"
+        macports_version: "2.6.4"
+        macports_pkg_version: "1"
         macports_mac_release: "11-BigSur"
 
     - role: node
@@ -358,8 +359,9 @@
     - role: teensy-loader
       tags: [desktop-applications, bespoke-pkg, teensy-loader]
 
+    # DISABLED: the YNAB 4 binary isn't available in the YNAB website anymore.
     - role: ynab
-      tags: [desktop-applications, bespoke-pkg, ynab]
+      tags: [disabled, desktop-applications, bespoke-pkg, ynab]
       vars:
         ynab_version: "4.3.855"
 
@@ -476,8 +478,10 @@
     # Virtualization, provisioning, containers and system tools #################
     #############################################################################
 
+    # DISABLED: not working on Big Sur yet:
+    # https://openzfsonosx.org/forum/viewtopic.php?f=20&t=3468
     - role: openzfs
-      tags: [system-tools, brew-cask-pkg, openzfs]
+      tags: [disabled, system-tools, brew-cask-pkg, openzfs]
 
     - role: virtualbox
       tags: [system-tools, bespoke-pkg, virtualbox]
diff --git a/roles/elgato-dock/tasks/main.yml b/roles/elgato-dock/tasks/main.yml
index 13e2d2b..e9082db 100644
--- a/roles/elgato-dock/tasks/main.yml
+++ b/roles/elgato-dock/tasks/main.yml
@@ -8,3 +8,5 @@
   command: >
     installer -package "{{ downloads_directory}}/Elgato_Thunderbolt_Dock_Software_{{ elgato_dock_version }}.pkg" -target /
   become: yes
+  # NOTE: ignoring errors because installing this seems to fail sporadically.
+  ignore_errors: yes
diff --git a/roles/fish-foreign-env/tasks/main.yml b/roles/fish-foreign-env/tasks/main.yml
index e23f7f7..293b1c1 100644
--- a/roles/fish-foreign-env/tasks/main.yml
+++ b/roles/fish-foreign-env/tasks/main.yml
@@ -9,4 +9,3 @@
   git:
     repo: "https://github.com/oh-my-fish/plugin-foreign-env.git"
     dest: "{{ home_directory }}/.config/fish/plugin-foreign-env"
-    version: "{{ fish_foreign_env_version }}"
diff --git a/roles/google-chrome-as-default-browser/tasks/main.yml b/roles/google-chrome-as-default-browser/tasks/main.yml
index 54d732d..81d0013 100644
--- a/roles/google-chrome-as-default-browser/tasks/main.yml
+++ b/roles/google-chrome-as-default-browser/tasks/main.yml
@@ -1,8 +1,3 @@
 ---
-- name: Check if Google Chrome is the default browser
-  command: defaultbrowser
-  register: is_google_chrome_the_default_browser
-
 - name: Make Google Chrome the default browser
-  command: defaultbrowser -set chrome
-  when: "is_google_chrome_the_default_browser.stdout.find('Current: chrome') == -1"
+  command: defaultbrowser chrome
diff --git a/roles/graalvm/tasks/main.yml b/roles/graalvm/tasks/main.yml
index d19b554..df77dc6 100644
--- a/roles/graalvm/tasks/main.yml
+++ b/roles/graalvm/tasks/main.yml
@@ -1,17 +1,17 @@
 ---
 - name: Download GraalVM
   get_url:
-    url: "https://github.com/oracle/graal/releases/download/vm-{{ graalvm_version }}/graalvm-ce-darwin-amd64-{{ graalvm_version }}.tar.gz"
+    url: "https://github.com/graalvm/graalvm-ce-builds/releases/download/vm-{{ graalvm_version }}/{{ graalvm_archive }}"
     dest: "{{ downloads_directory }}/{{ graalvm_archive }}"
 
 - name: Extract GraalVM
   unarchive:
     src="{{ downloads_directory }}/{{ graalvm_archive }}"
     dest="{{ downloads_directory }}"
-    creates="{{ downloads_directory }}/{{ graalvm_directory }}"
+    creates="{{ downloads_directory }}/{{ graalvm_extracted_directory }}"
 
 - name: Install GraalVM
-  command: cp -R "{{ downloads_directory }}/{{ graalvm_directory }}" "/Applications/GraalVM-{{ graalvm_version }}.app"
+  command: cp -R "{{ downloads_directory }}/{{ graalvm_extracted_directory }}" "/Applications/GraalVM-{{ graalvm_version }}.app"
 
 - name: Install native-image utility
   command: /Applications/GraalVM-{{ graalvm_version }}.app/Contents/Home/bin/gu install native-image
diff --git a/roles/graalvm/vars/main.yml b/roles/graalvm/vars/main.yml
index 76418dd..10d146e 100644
--- a/roles/graalvm/vars/main.yml
+++ b/roles/graalvm/vars/main.yml
@@ -1,3 +1,5 @@
 ---
-graalvm_archive: "graalvm-ce-darwin-amd64-{{ graalvm_version }}.tar.gz"
-graalvm_directory: "graalvm-ce-{{ graalvm_version }}"
+graalvm_java_version: "java11"
+graalvm_directory: "graalvm-ce-{{ graalvm_java_version }}-darwin-amd64-{{ graalvm_version }}"
+graalvm_archive: "{{ graalvm_directory }}.tar.gz"
+graalvm_extracted_directory: "graalvm-ce-{{ graalvm_java_version }}-{{ graalvm_version }}"
diff --git a/roles/gron/tasks/main.yml b/roles/gron/tasks/main.yml
index 2612e9b..1ac14fb 100644
--- a/roles/gron/tasks/main.yml
+++ b/roles/gron/tasks/main.yml
@@ -1,7 +1,7 @@
 ---
 - name: Download and install gron binary
   unarchive:
-    src: https://github.com/tomnomnom/gron/releases/latest/download/v{{ gron_version }}/gron-darwin-amd64-{{ gron_version }}.tgz
+    src: https://github.com/tomnomnom/gron/releases/download/v{{ gron_version }}/gron-darwin-amd64-{{ gron_version }}.tgz
     dest: /usr/local/bin
     mode: u+x
     remote_src: yes
diff --git a/roles/kubectl-tree/tasks/main.yml b/roles/kubectl-tree/tasks/main.yml
index 82e4d63..42eebd2 100644
--- a/roles/kubectl-tree/tasks/main.yml
+++ b/roles/kubectl-tree/tasks/main.yml
@@ -1,3 +1,3 @@
 ---
 - name: Install kubectl-tree
-  command: kubectl krew install tree
+  command: kubectl-krew install tree
diff --git a/roles/mac-ports/vars/main.yml b/roles/mac-ports/vars/main.yml
index 16812e6..2505c70 100644
--- a/roles/mac-ports/vars/main.yml
+++ b/roles/mac-ports/vars/main.yml
@@ -1,2 +1,2 @@
 ---
-macports_pkg: MacPorts-{{ macports_version }}-{{ macports_mac_release }}.pkg
+macports_pkg: MacPorts-{{ macports_version }}_{{ macports_pkg_version }}-{{ macports_mac_release }}.pkg
diff --git a/roles/mpd/tasks/main.yml b/roles/mpd/tasks/main.yml
index 93f7f49..7017969 100644
--- a/roles/mpd/tasks/main.yml
+++ b/roles/mpd/tasks/main.yml
@@ -3,7 +3,6 @@
   homebrew:
     name: mpd
     state: latest
-    install_options: with-libshout,with-lame,with-flac,with-lastfm
 
 # FIXME: this seems to fail if the service is already started.
 - name: Create mpd service and start mpd
diff --git a/roles/openzfs/vars/main.yml b/roles/openzfs/vars/main.yml
deleted file mode 100644
index 38f5ff2..0000000
--- a/roles/openzfs/vars/main.yml
+++ /dev/null
@@ -1,4 +0,0 @@
-openzfs_dmg: "OpenZFS_on_OS_X_{{ openzfs_version }}.dmg"
-openzfs_dmg_url: "https://openzfsonosx.org/w/images/{{ openzfs_image_path }}/{{ openzfs_dmg }}"
-openzfs_volume: "OpenZFS on OS X {{ openzfs_version }}"
-openzfs_pkg: "OpenZFS on OS X {{ openzfs_version }} {{ openzfs_macos_version }}.pkg"
diff --git a/roles/virtualbox/tasks/main.yml b/roles/virtualbox/tasks/main.yml
index c2d2469..1dd7626 100644
--- a/roles/virtualbox/tasks/main.yml
+++ b/roles/virtualbox/tasks/main.yml
@@ -10,18 +10,18 @@
   ignore_errors: yes
 
 - name: Mount VirtualBox image
-  command: >
-    chdir={{ downloads_directory }}
-    hdiutil attach -nobrowse VirtualBox-{{ virtualbox_version }}-{{ virtualbox_build }}-OSX.dmg
-    creates=/Volumes/VirtualBox
-  when: virtualbox_version_output.stdout.find('VirtualBox Manager ' ~ virtualbox_version) == -1
+  command:
+    chdir: "{{ downloads_directory }}"
+    cmd: "hdiutil attach -nobrowse VirtualBox-{{ virtualbox_version }}-{{ virtualbox_build }}-OSX.dmg"
+    creates: /Volumes/VirtualBox
+  when: virtualbox_version_output.rc != 0 or virtualbox_version_output.stdout.find(virtualbox_version) == -1
 
 - name: Install VirtualBox
   command: >
     installer -package /Volumes/VirtualBox/VirtualBox.pkg -target /
   become: yes
-  when: virtualbox_version_output.stdout.find('VirtualBox Manager ' ~ virtualbox_version) == -1
+  when: virtualbox_version_output.rc != 0 or virtualbox_version_output.stdout.find(virtualbox_version) == -1
 
 - name: Unmount VirtualBox image
   command: hdiutil detach /Volumes/VirtualBox
-  when: virtualbox_version_output.stdout.find('VirtualBox Manager ' ~ virtualbox_version) == -1
+  when: virtualbox_version_output.rc != 0 or virtualbox_version_output.stdout.find(virtualbox_version) == -1
diff --git a/roles/vlc/tasks/main.yml b/roles/vlc/tasks/main.yml
index a9b6f18..965f80e 100644
--- a/roles/vlc/tasks/main.yml
+++ b/roles/vlc/tasks/main.yml
@@ -1,19 +1,19 @@
 ---
 - name: Download VLC
   get_url:
-    url: http://get.videolan.org/vlc/{{ vlc_version }}/macosx/{{ vlc_dmg }}
+    url: "https://get.videolan.org/vlc/{{ vlc_version }}/macosx/{{ vlc_dmg }}"
     dest: "{{ downloads_directory }}/{{ vlc_dmg }}"
 
 - name: Mount VLC image
-  command: >
-    chdir={{ downloads_directory }}
-    hdiutil attach -nobrowse {{ vlc_dmg }}
-    creates=/Volumes/{{ vlc_volume }}
+  command:
+    chdir: "{{ downloads_directory }}"
+    cmd: hdiutil attach -nobrowse "{{ vlc_dmg }}"
+    creates: "/Volumes/{{ vlc_volume }}"
 
 - name: Copy VLC.app to Applications directory
-  command: >
-    cp -R /Volumes/{{ vlc_volume }}/VLC.app /Applications
+  shell: >
+    rm -rf /Applications/VLC.app && cp -R "/Volumes/{{ vlc_volume }}/VLC.app" /Applications
   become: yes
 
 - name: Unmount VLC image
-  command: hdiutil detach /Volumes/{{ vlc_volume }}
+  command: hdiutil detach "/Volumes/{{ vlc_volume }}"
diff --git a/roles/vlc/vars/main.yml b/roles/vlc/vars/main.yml
index b170356..d34d2b6 100644
--- a/roles/vlc/vars/main.yml
+++ b/roles/vlc/vars/main.yml
@@ -1,4 +1,4 @@
 ---
-vlc_name: vlc-{{ vlc_version }}
+vlc_name: vlc-{{ vlc_version }}-intel64
 vlc_dmg: "{{ vlc_name }}.dmg"
-vlc_volume: "{{ vlc_name }}"
+vlc_volume: "VLC media player"
diff --git a/roles/yapf/tasks/main.yml b/roles/yapf/tasks/main.yml
index 405f8d9..cd82307 100644
--- a/roles/yapf/tasks/main.yml
+++ b/roles/yapf/tasks/main.yml
@@ -2,5 +2,4 @@
 - name: Install Yapf
   pip:
     name: yapf
-    version: "{{ yapf_version }}"
     extra_args: --user