Yep. Upgraded to ios16 earlier today. Checked in. And can't save boarding pass to Apple Wallet. When I try i get a popup that reads "United Airlines: Error saving boarding pass to Apple Wallet."
I expect this is a bug caused by ios16?
Also got some sort of cryptic warning that items in wallet will "not automatically update."
Suggest you go in and provide "App Feedback" and report it as a bug.