I first thought this was an issue with my eyes, but I noticed this does not happen in 1.21.1. It might also be graphics card specific, but I cannot test this with another computer right now. A video of the bug is attached (hopefully it is clear enough).
Steps to reproduce:

1. Set the time to midnight.
2. Look closely at the ground (I used grass blocks) or an entity (I used a husk).
3. Everything flickers subtly.