Wow, they have a C# 12 now? I wrote "old versions of C#" because I last delivered a project in C# 3.5, and honestly that was maybe 12 years ago and it was a bit arrogant of me to add it, I don't think I understand C# _that_ well.
.NET Native is dead for a long time, it’s the least important runtime flavour compared to others today because of this. IL2CPP and Mono are orthogonal and only ever relevant if you develop for Unity going forward (okay, there’s Blazor too which uses it for WASM).
No it isn't, given the extent UWP is still used on Windows given the failure of WinUI 3.0/WinAppSDK to deliver something that has feature parity with it.
Windows widgets and the new badly implemented File Explorer are probably the only WinUI 3.0 applications, the remaining stuff is still pretty much UWP, while many third parties that still care about WinRT at all, are stuck in UWP due to missing features and tooling in WinUI 3.0/WinAppSDK.
As for the rest of your remark, it doesn't change the fact that those runtimes exist and have relevant differences.
Bonus points for the ones that have different behaviour between .NET Framework and Core.
Extra bonus points when taking Mono, .NET Native, IL2CPP into consideration.