Is there a solution?
Short answer: YouTube probably considers this a feature and not a bug.

Problem: Screen darkening at the beginning of replaying a video clip:
A user watching videos at the YouTube.com/@aslu site mentioned that they don't
like it when the videos go dark when they try to watch the video a second time.
Attempted Solution:
Check to see if "ambient mode" is turned on in your YouTube watch settings.
You can turn off YouTube's Ambient Mode in a few simple steps, whether you're on
a computer or a mobile device.
On a Desktop:
Open YouTube: Go to the YouTube website in your web browser.
Start a video: Play any video to access the player settings.
Click the gear icon: Hover over the video player to see the controls, then click
the gear icon (Settings).
Find Ambient Mode: In the settings menu, locate the "Ambient mode" option.
Toggle it off: Click the toggle switch next to Ambient mode to turn it off.
On a Mobile Device (Android or iOS):
Open the YouTube app: Launch the YouTube app on your phone or tablet.
Start a video: Play a video to access the player settings.
Tap the gear icon: Tap the video screen to show the playback controls.
Then tap the gear icon in that list ("More" or "Settings") to select additional
settings.
Find Ambient mode: Locate the "Ambient mode" option.
Toggle it off: Tap the toggle switch to turn Ambient mode off for all videos.
Update:
The solution did not work for me. Despite turning off ambient mode I notice that
YouTube videos -- when replayed on a Pixel (or Android) phone in the YouTube web
interface -- still dim during the first bit of replay time. The ambient
mode issue is a separate issue.
Update:
When paused, a YouTube video tends to dim. You can tap part of the dimmed
paused video frame that is not right on any of the control buttons that appear
over the dimmed video when the video is paused, and the dimming filter and
view-obstructing controls disappear (temporarily at least). While not a
perfect or full solution, it does help a person get a good look at a paused
frame of a YouTube video.
Notes:
█