Moguri mod works great on the Steam deck. It’s a bit of a learning curve to get it installed, but there’s a guide that will take you through the entire process, and it will teach you some about the more niche features of the deck.

There is! 7th Heaven is what you want.

https://7thheaven.rocks

This is more like a huge mod manager that lets you pick and choose the mods you want, rather than Moguri Mods install and it just works.