So for whatever reason you want the .NET runtime over Mono - not sure why that is a hard requirement, but AFAIK that is also the goal for microsoft. As in, merging those runtimes and have a single codebase that works for all platforms (including android). There are technical obstacles and historic codebases, but I would expect this unified runtime soon.
Cause since .Net Core 3 (first real production ready cross platformness) to .Net 10 (current LTS) is light years ahead of .Net Framework 4.8 / Mono (which is like half the performance of old .Net 4.8..). Not to be crude, but mono is pretty much trash. Should just be deprecated and the engine bro's should just stick to .Net LTS version (8 or 10, but 8 will be dead in a year). .Net 8/10 also has much better build tools, cleaner & smaller executables, better packaging tools to make deployments a breeze over the old system. The compiler is also much faster in general. You can tree-shake the hell out of your builds to get very lean artifacts. And then there is the garbage collector. And all of the low level optimizations in the CLR that just makes everything fast & less memory hungry.
Unity should really create a version of their engine on .Net 10, make the core as platform-agnostic as possible. It's fine if this variant is not backwards compatible. .Net 10 is also already on Xbox.
