Hello PhilippKathöfer,
We understand that after updating your Apple Watch, it continues to unlock. This behavior could be related to the software. In that case, we'd like to provide you with a few steps that can often resolve software-related issues:
- Restart Apple Watch. This allows for your device and the software to be refreshed.
- Unpair and erase your Apple Watch. Unpairing your Apple Watch restores it to its factory settings.
("Before erasing all content and settings on your Apple Watch, your iPhone creates a new backup of your Apple Watch. You can use the backup to restore a new Apple Watch. After your Apple Watch unpairs, you'll see the Start Pairing message")
Also, you mentioned that you were using watchOS 9.3. This appears to be a beta version. If you're running beta software, you should send Apple your feedback and report bugs. Here's how: Bug Reporting - View Feedback Assistant
Let us know if this helps.
Have a wonderful day!