This update 'forces' the combined view and filters most Teams and is quite frankly awful.
Undoing "Settings > Chats and Channels > Viewing chats and channels" does not undo the damage done by this change, When you switch the view off, you are still left with a filtered view of Teams that is different than before that requires multiple clicks to undo. It is much worse than the previous UI which defaulted to 'show' and left it to the user to hide.
This update assumes that you only want to see teams you're actively participating in. It does not consider workloads where occasional check-ins are needed (War-Room Teams, Bi-Annual Check in teams, Teams for alerts, Teams used for quarterly reporting (think Taxes)).
For me personally, I just spent 20+ minutes going through multiple clicks to 'undo' the carte blanche hiding. I dread training my users on it.