> That's not to say that you couldn't write a commercial game engine with something like C# that stands shoulder-to-shoulder with unity and unreal, but it doesn't seem like anyone has attempted to do so.

Stride should mostly fit the bill: https://github.com/stride3d/stride

Their homepage: https://www.stride3d.net/

Even the physics engine they use is in C#: https://github.com/bepu/bepuphysics2

Not a very popular game engine (never got the attention that the likes of Godot did), but it's nice to work with! It’s up there with Stride in regards to the “indie” game engines I like, maybe alongside jMonkeyEngine (since you typically don’t see that many Java game engines either).