A: To use the Smartspacer widget with no integration, root is never required. However, if you want to use enhanced mode, which integrates with the system where available, you will need either Shizuku/ADB (Android 12+) or root (Android 10-11)
A: This is due to the method used to replace the system Smartspace service, while maintaining the original service (also known as At a Glance). While it would be possible to set Smartspacer as the default on a rooted device with an overlay, it would break compatibility with At a Glance, so the preferred method is to simply require a one-tap setup per reboot.
A: Currently, to use it on release versions of launchers, you have to use Discover Killer, which requires root. However, there is a test version of Lawnchair with the functionality replaced (no root needed), and it may eventually be merged into Lawnchair's mainline builds. Other launchers may also add it as an option in the future too.
A: Open an issue, using the Bug Report option.
A: In the Plugins tab of the app, there are a number of available plugins. If you have an idea for a plugin which may work, request it at https://github.com/KieronQuinn/SmartspacerPlugins/issues
A: Check the OEM Smartspace page