I was surprised to see this extreme usage of Find My data. It must have happened in the last few days. The reporting period was roughly 60 days. When I reset it Find My used another 16 MB in 30 minutes without WiFi. That seems to be a lot.
Only change was to add a single shared AirTag. And that does not even update reliably.
Update:
https://preview.redd.it/6t6lkrk36f1c1.jpeg?width=1170&format=pjpg&auto=webp&s=f6427d7d2d4d403f9012c6f047b3e19b74b8f712
Roughly 24 hours later: 123 mb per day. Wow.