Compiling existing C# code to WebAssembly

Question

Is it possible to compile existing C# code to WebAssembly (.wasm) so that no or nearly no code changes have to be done?
Do I have to use Blazor for it or are their other possibilities?

Answer 1

Is it possible to compile existing C# code to WebAssembly (.wasm)

No, there is no compiler (yet). But

so that no or nearly no code changes have to be done?

That is easy, you can simply add .net DLLs (packages) to your project.
Just make sure that the code makes sense in a Browser, ie no Threading, no I/O except HttpClient etc.

Do I have to use Blazor for it or are their other possibilities?

For now there is only Blazor.