rowdy

If you have access to a Windows machine, that is the easiest method. Setup everything as you want it, with Mod Organizer 2 (portable), on the Windows machine. Then use the Linux installer of MO2 on your Steam Deck. Overwrite the contents on your Deck with the directories from your Windows machine. You may need to mess with the path arguments in Steam to open MO2 when running Fallout.

I’ve heard you can mod directly from the Deck, but it’s more tedious. I haven’t done it this way, so I have no advice.

It took everything in my power to not downvote this, but given the thread I gave an upvote instead.