I’ve never found a Nexus Mods alternative mirror. There are other sites that host mods, you might be able to find what you’re looking for.

https://www.moddb.com/games/fallout-new-vegas/mods

https://gamebanana.com/games/3824

Halo Infinite has free multiplayer that is cross-platform between PC and Xbox, and works on the Steam Deck. There are lots of competitive and co-op modes available, both in official playlists and community made Forge modes.

You can make private matches until you’re comfortable joining public ones.

The campaign is also online co-op, but must be paid for.