Hello tomgoosmann,
It looks like you have already done some great troubleshooting to get your Apple Watch to unlock your Mac.
One thing you want to be sure of is that the password for the user account on the Mac being unlocked only contains upper or lowercase letters, numbers from 0 to 9, underscores, hyphens, or periods. Any other special characters can prevent the Apple Watch from unlocking the Mac.
Another thing to try is to turn would be to test in safe mode. This will help isolate this issue.
To start in safe mode, follow these steps:
1. Turn on or restart your Mac, then immediately press and hold the Shift key as your Mac starts up.
2. Release the key when you see the login window, then log in to your Mac.
3. You might be asked to log in again. On either the first or second login window, you should see ”Safe Boot” in the upper-right corner of the window.
More information is available here: How to use safe mode on your Mac
The computer will take longer to start in safe mode, and the screen may have some distorted video as it starts up. This is normal. Once you are logged in, use the system and test to see if the issue continues.
If everything seems to work as expected, go ahead and restart the computer normally and test again. Starting in safe mode forces the computer to run some disk checks similar to First Aid. This can resolve some issues.
Cheers.
