Working on an audio port at https://github.com/ottohg/pokeemerald-wasm, and I've gotten pretty far. It's working, but there are just accuracy and instrument issues that need to be sorted out before it's in a playable state.
The question is - how do you intend to verify whether an application is official or unofficial? What's stopping the official application to be 'patched' with a fake signature feigning validity?
It's very unlikely that performance would be hindered by a particular Linux distribution, but usually rather the desktop environment that it employs. NixOS with LXQt would run very differently to NixOS with GNOME.