Hi there CPPVB,
Are you adjusting the brightness on your Apple Watch Ultra with the steps below?
Open the Settings app
on your Apple Watch Ultra, then tap Display & Brightness to adjust the following:
* Brightness: Tap the Brightness controls to adjust, or tap the slider, then turn the Digital Crown.
You'll find this information here: Adjust brightness, text size, sounds, and haptics on Apple Watch Ultra - Apple Support
Also, you'll want to be sure the Apple Watch and its paired iPhone are both update to the latest software versions, which are watchOS 10.0.2 and iOS 17.0.2. If needed, learn how to update from the links below:
Update your iPhone or iPad - Apple Support
Update your Apple Watch - Apple Support
Next, have you tried using Night Mode to see if that helps? Learn more about that here: Apple Watch Ultra, built for the outdoors - Apple Support
If this behavior persists, you'll want to reach out to Apple Support directly for further assistance. They're best-equipped to take a closer look at the issue and provide some additional guidance. This link will help you get started: Apple Support
Take care.