You are barking up the wrong tree.

You are saying that your Steam Deck is not working with the wifi at your home but there is no issue with it working with airport, in-flight, and hotel wifi.

That immediately tells me that there is no issue with your Steam Deck but the POS router that your ISP has provided.

You need to:

A: call your ISP and get them to fix their broken POS router.

B: At a later time get your own wifi router then call your ISP to put their useless shit into bridge mode so you can use your own router.