Just Google "are airtags allowed on planes".
I bought my AirTag in February and so far have used it on a couple of flights and a cruise and it performed well, although it seems to take a few minutes to orientate itself as it moves from place to place.
See no reason why it shouldn't be used on my checked bag. All stories I can see about lithium in batteries or Bluetooth transmitting in flight have been thoroughly de bunked.
Still debating whether to get more, as usually have 4 items of checked luggage when travelling to the USA.