Disclaimer: I don’t own a steam deck but have used Linux for the last couple years.

I did a quick search and appears for the last couple years people have reported updating decky [1] [2] and experiencing the same thing, it seems you’re able to rollback to a previous version that works or you can attempt at factory resetting.

Personally if it were me, given that SteamOS is Arch Linux based I would dig into the Arch Linux wifi driver documentation and see if you can attempt at reinstalling the driver however, given that I do not know which repositories the Steam Deck pulls from and that I do not know if you use the Arch drivers I would advise caution before jumping into this path, it is possible the wifi driver used by the Steam Deck isn’t from the Arch Linux repo’s and from valves own repo’s and installing a second driver on-top of that one may cause a package conflict and those certainly aren’t fun to fix!

Hope this points ya in the right direction.