Novaliss
When first time reading the title, I thought it's one more spam post, while reading your question, I thought that's rather a question for my Home Assistant forum, until I understood what you want. So much for the funny part. 😹
I think you could use a normal necklace for your cat and buy a normal, small, privacy friendly "find my" Bluetooth pendant and attach it to the necklace. I don't think that GOS supports "find my" stuff natively, but via the pendant's app.
I was looking on F-Droid, but found nothing for the moment. There is an app called "BLE radar", but I think this app isn't for remote tracking. Maybe there are others, elsewhere.
Also answering this because I love cats.