I'd be ecstatic if there were something checking those boxes that wasn't owned by Microsoft.
However I would point out that before Unity took off, jMonkeyEngine had a good following.
And since reference counting is also garbage collection from CS point of view, I would add Swift with the game development kits, however that is pretty much Apple only, thus not really the same league.
Microsoft unfortunately since XNA, the whole DirectX team has been anti .NET, they didn't even provided Windows Runtime Components for .NET Native, even though it would have been relatively easy to do so, as it is based on COM (plus some extras).
The moment key people responsible for XNA left the building, it was done.
Game developers usually are the last ones to move, and tend to do so due to external factors, mostly pressed by platform owners.
It was like that when we moved from Assembly in 8 and 16 bit platforms, slowly into Object Pascal (Mac/PC) and C.
Then it took until Watcom C/C++ on PC, and PlayStation 2 SDK, for C++ to finally start being taken seriously by game devs, then XBox did the rest on console space.
C# had a first victory in 2004 with Arena Wars, in OpenGL
https://en.m.wikipedia.org/wiki/Arena_Wars
Managed DirectX was already around, then XNA on XBox Live Arcade was the needed push.
When Microsoft killed in name of C++ and replaced it with DirectX TK, as usual in Windows in their territorial attitude, Mono project came up with MonoGame as rescue.
This is what enabled them to eventually join efforts with Unity, when they were rewriting the engine to be cross platform, and go beyond OS X.
Eventually Unity alongside C#, use to have a certain Flash like vibe, and for many, the entrypoint into the .NET ecosystem.
So it is kind of sad see this go away.
I don't believe in the one true language for everything, other than Timex BASIC, the moment I learned Z80, I have been a polyglot ever since.
A cool designed game, even in PyGame, has probably more entertainment value, than yet another remake in Unreal running on a PlayStation 5 Pro.
It's such a pleasure to write in C# and you know that you won't get dumb ninja issues because of pointers or types.