FYI, I finally found an actual date for the AT&T shutdown, Feb 22 2022. Looks like I will know in 20 days if I have to switch to T-Mobile or get a new phone.
I got myself a 99 cent Mint Mobile sim card off amazon which comes with a free 7 day trial / 250 mins / 250 text to test out the T-Mobile network coverage.
ATT has my imei registered as an att branded blackberry priv (which is on the approved list) since they don't recognize the fxtec imei in their system (invalid)...but of course they know what my sim is actually in. Only time will tell at this point.