New tires and check pressure light is on and pressure is correct.
It’s likely one of the pressure sending units has a dead battery. You’ll need to have s new unit installed since the batteries aren’t replaceable. Too bad it wasn’t acting up before you bought new tires. I paid a bit over $90 to have one replaced on a Corolla.
As Dave said, or there might be a tire pressure reset or relearn procedure required. Check your owners manual.
I don’t think your Audi has sensors in the tires. Mine doesn’t. It uses the ABS sensors. The owners manual…that book in the glove box… tells you how to reset the TPMS system. It needs to be done at least once a year. It is very easy.
Some cars also monitor the spare tire, so make sure that pressure is correct too.
Do any cars come with a full size spare tire? Compact spare tires are not monitored by the TPMS.