- `Get-ExperimentalFeature` no longer has `-ListAvailable` switch (#8318)
- `Debug` parameter now sets `DebugPreference` to `Continue` instead of `Inquire` (#8195) (Thanks @KirkMunro!)

* Engine Updates and Fixes

- Improve PowerShell startup time by 24% (#8341) (#8396)
- Remove extra newlines from formatting which resulted in unnecessary double newlines (#8247)
- Add `Enable-ExperimentalFeature` and `Disable-ExperimentalFeature` cmdlets (#8318)
- Fix `Export-ModuleMember` bug for a `ScriptBlock` having no context (#8363)
- Fix race condition to access `powershell.config.json` (#8249) (Thanks @iSazonov!)
- Add `SkipCA` and `SkipCN` check requirement to WinRM/OMI HTTPS connection (#8279)
- Add fix for `Start-Job` initialization script which should not be executed as trusted in system lockdown (#8284)

* General Cmdlet Updates and Fixes

- Add `Enable-ExperimentalFeature` and `Disable-ExperimentalFeature` cmdlets (#8318)
- Add cmdlet `Join-String` for creating text from pipeline input (#7660) (Thanks @powercode!)
- Expose all cmdlets from `PSDiagnostics` if `logman.exe` is available (#8366)
- Fix `Get-Help` for advanced functions with MAML help content (#8353)
- Conditionally mark getter/setter implementations as virtual in generated classes (#8303) (Thanks @IISResetMe!)
- Fix for `PSDrive` creation with a UNC path with a trailing backslash or forward slash when combined with `-Persist` (#8305) (Thanks @kvprasoon!)
- Remove `Persist` parameter from `New-PSDrive` on non-Windows platform (#8291) (Thanks @lukexjeremy!)
- `Test-Path`: Return `$false` when given an empty or `$null` `-Path`/`-LiteralPath` value (#8080) (Thanks @vexx32!)
- Token calculation fix for `Get-Help` executed on `ScriptBlock` for comment help. (#8238) (Thanks @hubuk!)
- Support `Get-PSHostProcessInfo` and `Enter-PSHostProcess` on Unix platforms (#8232)

* Code Cleanup

- Update `resgen`, `typegen` to use .Net Core 2.1 (#8369) (Thanks @bergmeister!)
- Change `Newtonsoft` deserializing bug comment to link to the new issue (#8377) (Thanks @louistio!)
- Cleanup `#if !CORECLR` code (#8337) (Thanks @iSazonov!)
- Cleanup `UpdatableHelpSystem` and enable XSD validation on MAML help content (#8335) (Thanks @iSazonov!)
- Remove old `customPSSnapInType` parameter from `PSSnapInInfo()` (#8333) (Thanks @iSazonov!)
- Cleanup `#if CORECLR` from some files (#8332) (Thanks @iSazonov!)
- Cleanup `AssemblyInfo` (#8190) (Thanks @iSazonov!)
- Fix `GetLocationCommand` output type parameter set and style issues (#8324) (Thanks @Meir017!)

* Tools

- Remove `dependabot` attribution and generate changelog sections using `CL-*` labels (#8386)

* Tests

- Update folder path for storing optimization profile and add test to validate loaded assemblies and libraries on startup (#8406)
- Fix an intermittent failure in macOS logging tests (#8385)
- Created a `csproj` to pin test modules and updated `build.psm1` accordingly (#8350)
- Update help content for `TabCompletion` tests only if it does not exist (#8355)
- Skip `Enter-PSHostProcess` tests on `AppVeyor` due to `PSReadline` issue (#8317)

* Build and Packaging Improvements

- Remove `AmazonLinux` Dockerfile (#8271) (Thanks @kiazhi!)
- Make `install-powershell.sh` auto-detect if it should use `wget` or `curl` (#8225) (Thanks @DarwinJS!)
- Bump `NJsonSchema` from `9.12.2` to `9.13.1` (#8319) (#8328) (#8412) (#8371) (#8384)
- Bump `Microsoft.PowerShell.Native` from `6.2.0-preview.2` to `6.2.0-preview.3` (#8411)
- Update the name of the artifact to be unique per artifact (#8405)
- Create unified release build for macOS and Linux packages (#8399)
- Add Linux `ARM64` build support (#8016) (Thanks @slide!)
- Update the timeout of CI builds (#8398)
- Bump `PackageManagement` from `1.2.2` to `1.2.4` in `/src/Modules` (#8320) (#8383)
- Bump `Newtonsoft.Json` from `11.0.2` to `12.0.1` (#8348)
- Enable pipeline to sync `PSGallery` modules to `AzArtifacts` feed (#8316)
- Build Alpine `tar.gz` package in release builds (#8340)
- Publish test package to `AppVeyor` daily build (#8273)
- Bump `Microsoft.CodeAnalysis.CSharp` from `2.9.0` to `2.10.0` (#8294)
- Bump `PowerShellGet` from `2.0.1` to `2.0.3` in `/src/Modules` (#8321)
- Enable `Open Here` context menu on Windows to work with root of a drive (#8287)
- Bump `System.Data.SqlClient` from `4.5.1` to `4.6.0` (#8266)

* Documentation and Help Content

- Merge `changelogs` from `6.1.1` and `6.0.5` into master (#8283)
- Remove all reference to `AppVeyor` and `Travis CI` from docs (#8376)
- Change default issue template to use different categories (#8203)