Will I have to notify Att when I get S22 ultra to activate my plan to 5g?
you don't have to upgrade to a 5G plan if you buy your phone outright
Which I do, so it will automatically show up as 5g on the phone?
No, it wont because you don't have a 5G plan; you have to upgrade the plan to get 5G. However, because you bought the phone outright, you aren't forced to upgrade the plan but that doesn't mean you'll automatically get 5G service.
Verizon must be different. When I turn off WiFi at home I get the 5G instead of the 4LTE I used to get. I am on an unlimited talk and text plan and have not changed it in over 5 years.