The original statement from Lufthansa mentioned that Airtags fall under the category of "Dangerous Goods". "Dangerous Goods" is a term used by the ICAO to refer to batteries or items with batteries (also refers to dangerous chemicals or radioactive material, but if you look at ICAO guidance about Dangerous Goods, the bulk of the guidance is about batteries).

> Hundreds of tags transmitting is bad for the same reason that phone's have to be shut off during flights.

Phones don't have to be shut off during flights. That hasn't been a thing for years.

Any given commercial flight has hundreds of phones, wireless headphones, tablets, smartwatches, etc all transmitting radio signals at significantly higher power than Airtags.