I need to know which games I should practice, because I almost started practicing any% for 3D Land in emulator, which isn't allowed sadly. (Also is there any way I could request emulator specific categories for games that don't accept emulators?)

You should ask in the specific game forums, you are more likely to get help there.

Most of the fan games would be options:

https://www.speedrun.com/mario_fan_games

j ai une question je souhaite speedrun super mario bros puis je utiliser l'émulateur RetroArch pour speedrunn?

I just looked at Emote Challenge that one you can use emulators if I remember. Great rom h@ck too.