Unity is currently working to make Unity compatible with .NET 6 / CoreCLR, but they don't yet have a release date for that yet. The progress is being tracked in this megathread:
I agree, it seems like a huge effort. But if they reach their ultimate goal of shipping an unmodified version of .NET, it seems like that work would pay off:
https://forum.unity.com/threads/unity-future-net-development...