I just tested this on my older series 7, and in watchOS9, the rotate up from a black screen in Theater mode still works as described.
If scrolling your crown up in watchOS 10 is showing the screen up to show the complications, that means your screen was on to begin with.
To Clarify: I have an automation that turns on "Theater Mode" after I go to bed. This makes the Apple Watch always on feature turn off. When it is in Theater Mode, and the screen is black, you can rotate the Crown Up slowly to brighten the display one click at a time. Then from there you can tap the screen and the brightness setting will remain.
This rotation feature only turns the brightness up to the max that you have it set in Settings > Display.
Without theater mode on, I found that activating the "Flashlight" tool, and increasing its brightness will also increase the watches brightness if in a dark area. When you turn off the flashlight (screen bright white), the brightness of the screen setting is left at the brightest you had it set in Settings > Display.
Good luck!