Apple Watch brightness
I have had my Apple Watch for 9 months with no issues. Suddenly, it is taking seconds if not minutes for the screen to brighten. Almost too dim to read. Have adjusted brightness in settings.
Apple Watch SE, watchOS 8
If you have seen a change in recent weeks it is possible Apple changed the speed of response to ramp up more slowly in the new version of software. I have not really noticed a problem until you mentioned it, but a quick test on my Watch Series 7 in near darkness followed by turning on the light showed brightness increasing at an acceptable rate, roughly 1-2 seconds to come to full bright with the light directly onto the watch face. With the light more from the side (so seeing bright walls rather than direct light) it was a little slower, up to about 3 seconds.