Is the GC in C# actually that much of a problem? Slay the Spire 2 is made with Godot + C# and the devs seem to be fine with it. Of course, it's probably not a computationally very demanding game but still the GC in C# does not seem to be a problem there.
Yes it is a big problem. StS devs cannot write normal C# code, you have to really work around the C# integration to avoid lag spikes. See my other comment GitHub thread. There's also things like this https://github.com/godotengine/godot/issues/86926 and that the underlying types aren't compatible (Godot collections) that make it clear they aren't serious with the C# support.
The other huge problem is the terrible external editor support, it does not work well at all. This means your vim, jetbrains, whatever muscle memory from a lifetime of professional dev work becomes useless, and you have to use a gimped text editor worse than notepad++. You can use an external editor, but then lots of things don't work very well, scenes get randomly corrupted, hot reloading doesn't work, etc. It's many issues like this that prove Godot's only priority is attracting and entertaining people who have never written code before, instead of making an engine viable for shipping games.
I gave Godot a real chance for years, but at the end of the day it's a toy. There's a good reason that there are barely any games using it, and they're all extremely technically simple; surprisingly, that reason is not an unsophisticated underlying engine, but rather a million DX papercuts that a good ambitious developer would just never accept.
I don't know about it's use in godot but it's obvious it's not a problem to shipping a good game
https://unity.com/blog/games/games-made-with-unity-2025-rele...