Good news - just woke up and started “Find my” on my iPhone 12 Pro. And what should I say, the issue is fixed at least with my Apple ID and all my devices. So somebody must have fixed, something. Thank you Apple…

After installing iOS 15 beta 2 - no change, same issue

Same issue - on all my devices iOS / iPadOS 15 beta devices as well as iOS 14 devices. Issue has started this morning after I Have reset my Apple Watch with watchOS 8. After repairing the issue with „Find my“ Unavailable - Unable to connect so server has started. So must be related to the Apple ID. On a different iOS device I‘m using another Apple ID and there are no issues.