Air New Zealand doesn’t allow trackers either - I expect most airlines don’t, so I don’t know why Lufthansa is getting shit here. Air NZ says: “Baggage Trackers (battery powered): Only battery powered baggage trackers that can be turned off i.e. are not in sleep mode, will be accepted in checked baggage. Some devices have an automatic On/Off feature, but not all. Always check the specifications of the device you want to buy as it may not be accepted by us. For those devices that have an auto On/Off feature, the tracking App must not be used in flight.” — https://www.airnewzealand.co.nz/travelling-with-lithium-batt...

FAA specifically allows non-rechargeable small Lithium cells if in equipment in checked baggage. However, the table on the second pages says that small battery/cell spares are not allowed in checked baggage. “Lithium metal batteries (a.k.a.: non-rechargeable lithium, primary lithium). These batteries are often used with cameras and other small personal electronics. Consumer-sized batteries (up to 2 grams of lithium per battery) may be carried. This includes all the typical non-rechargeable lithium batteries used in cameras (AA, AAA, 123, CR123A, CR1, CR2, CRV3, CR22, 2CR5, etc.) as well as the flat round lithium button cells.” — https://www.faa.gov/hazmat/packsafe/resources/media/Airline_...

Not OP but the point is that Li-ions are rechargeable and therefore more susceptible to shorting/thermal runaway than lithium batteries which are not wired to be rechargeable and therefor less at risk for shorting/thermal runaway.

People who investigated the claims of the article this one is replying to have found that the original source of this claim was a German article where someone called Lufthansa and asked this question. The answer they got from the Lufthansa representative was essentially citing an ICAO rule about devices with lithium batteries - which got twisted in this "Lufthansa doesn't allow AirTags" narrative.