There are special devices like BikeFinder[0] as well. Where I live it give you a reduced price on insurance. Worth it if you have an expensive e-bike for commuting etc that you often have to park outside. It has some more features than an airtag: It can phone home itself without being near a phone, can alert you the moment the bike is moved etc.
There are GPS collars for dogs that would seem more directly related to solving the problem. I spoke to a guy the other night with one and he said it cost 6 euros a month, which is going to add up. Fine for a dog, where you expect to loose him / her to an extent, whereas I assume you wouldn't expect to loose a bike.
[0]: https://bikefinder.com/