Re the airtag solution.
I left my briefcase on an inter-terminal shuttle bus at Barcelona airport. After all I had heard about luggage theft in Barcelona I feared the worst. I saw the air tag at the other terminal, so went back there. Just as I arrived, the tag showed up at the terminal I had just left! I finally figured out that the location doesn’t update that quickly and that the bag was clearly on a bus.
I ended up checking each bus as they came around. And finally, one driver greeted me with a big smile and handed the bag to me. He had put it behind his seat.
It was a nerve-wracking experience, but as long as I could see the bag was still in the airport, I had hope!