I don’t think the web output works with c# currently.

Be happy to find out I’m wrong.

I think it worked in the previous version.

The way unity solves this is with some kind of proprietary compiler. They translate the C# into C++, and then compile that into webassembly.

Whereas others (incl. Godot) need to ship the .NET runtime in the browser. (A VM in a VM.)

It makes me sad that Unity doesn't open source that. That would be amazing.