Yep you're right it was 2022. I was remembering that some places were claiming it would expire a year earlier than it really does so I added another year - but those places were claiming after the 2021 season. The 8 year extension deal was signed in 2014, starting in 2015.
So two more seasons left, then my guess is that AT&T keeps the commercial exclusive but residential becomes like MLBEI et al and available to any cable/satellite provider that wants to pay for it on a per customer basis. What they will do as far as streaming (i.e. run it themselves like MLB, or sell a streaming exclusive to someone) is anyone's guess.