Greetings!
We appreciate your post in the Apple Support Community.
It's possible that the issue you're experiencing with Apple Fitness & Health not syncing your Polar Beat App workouts is a bug.
Make sure you have the latest versions of both Apple Fitness & Health and the Polar Beat App installed on your iPhone.
Try to disconnect and then reconnect the Polar Beat App within the Health app to see if that triggers a sync.
If the issue persists, consider reaching out to Apple Support Tel.: 0800 6645 451 (DE) for assistance. They can provide you with specific troubleshooting steps or updates on any known issues.
For English speakers, we have a dedicated community right here: discussions.apple.com.
Since your message is in English, we warmly invite you to join us in that community.
Thank you!