You can use the app without location sharing enabled but it's unclear if they use the geolocation of your photos. Afaik an app has access the most recent taken photos, that might have changed with iOS 15.

I thought I read an article how Facebook is analysing dust on the camera lens to correlate photos, not in the product by Facebook research team. Can't find it. Apparently it's possible to identify fingerprints on photos https://www.researchgate.net/publication/339501227_Analysis_...