We now have an updated version of the FFXIDB plugin that works on Linux, including the Steam Deck.
It is currently in testing on the Dev launcher channel, but you can grab it and use it with Live as well. (If you don't know which channel you use, or you followed our Linux setup instructions, you're almost certainly on Live.)
You can grab it here:
https://update.windower.net/dev/plugins/FFXIDB.dll
If you're so inclined, please give it a try and let us know if you run into any problems with it. If there are no major issues reported, we'll probably roll it out to Live soon.