Hello GeosarGR,
Thanks for posting in Apple Support Communities. You've completed some great troubleshooting steps so far. To ensure that we're covering all of our bases, be sure that your Apple Watch is running the latest software version. Open the Apple Watch app on your iPhone, select My Watch > General > Software Update. If an update is available, tap Download and Install. Also, be mindful of the following details:
Make sure that your Apple Watch is compatible with the latest software: watchOS 8 is compatible with Apple Watch Series 3 and later and Apple Watch SE. Upgrading to watchOS 8 requires iPhone 6s or later running iOS 15 or later. Find your Apple Watch model.
Next, check these things:
1. Update your iPhone to the latest version of iOS.
2. Make sure that your Apple Watch is at least 50 percent charged.
3. Connect your iPhone to Wi-Fi.
4. Keep your iPhone next to your Apple Watch, so that they're in range.
It could take from several minutes to an hour for the update to complete. You might want to update overnight or wait until you have time.
More details found here: Update your Apple Watch
Let us know if this helps.
Best regards.