“the Apple Watch Ultra 2’s screen also gets dimmer than the first watch, going down to just one nit when you have the watch in sleep mode. It can also get that dim if the screen isn’t active and you’re in a really dark room. The ambient light sensor adjusts the brightness depending on the situation.”

It is dimmer making it hard to see what’s on the screen with old eyes. And there’s nothing you can do about it but hope (https://www.apple.com/feedback/watch/) they make it possible to disable the ambient light sensor and set the brightness manually.

That’s actually a good battery saving feature when asleep