No ROMs or BIOS files are provided, and the community on the Discord server is super helpful and responsive if you run into any issues.)
(All of this is perfectly legal and on the Microsoft Store, by the way. It's far and away, the most backwards-compatible console I've ever owned lol
Granted, N64 emulation is kinda screwy no matter where you do it, but I've played PSX, PS2, GameCube and Wii games with no noticeable issues. Then, you can go to that same link- on your Xbox in the Edge web browser, and follow the links to install RetroArch (and a few other things, besides. Then click the Discord link, join that, and wait for the next Whitelist announcement (usually a couple of times a day). Go there, click Whitelist at the top of the page, and fill out that form. If this interests, you, it's fairly easy to get RetroArch running on an Xbox, even without changing over to Dev Mode.