Some of the information here is outdated.
Blazor now uses mono-wasm AOT to compile to webasm using llvm. It also still supports an interpreted mode for rapid prototyping.
https://www.mono-project.com/news/2018/01/16/mono-static-webassembly-compilation/
Note that Blazor is really the app framework, you can use mono-wasm without Blazor, and probably want to in this case.
.net core 5 will support compile to webasm natively without the need to use mono