The error is telling you about unsupported MIME type. Did you check the actual MIME type? It should be Content-Type: application/wasm for .wasm files. I assume you have WebAssembly Streaming checkbox in the build settings checked since the error is about wasm streaming.
Also if you have GZIP Compression checkbox enabled, server has to have Content-Encoding: gzip response header set too.
If you don’t need wasm streaming or if you consider my blabbering gibberish, just try to disable WebAssembly streaming checkbox and GZIP Compression checkbox.