I'm pretty sure this also applies to Model 3s, not sure about S/X.
When you get that notification card saying there's someone not wearing the seat belt on the rear seats, especially when you fold the rear seats for a larger trunk or some object is on the seat, I just recently discovered you can click on the red icon, and that will make it change to a baby seat, muting the notifications!
Just thought I'd share it. Search brought nothing about it, and I've had this annoyance for 4 months until I learned how to fix it!
Cheers, y'all!