Whenever a tooltip is rendered on screen while in the player's inventory GUI, it causes the player's held item or hand to change the lighting and shadows. Occurs in both survival and creative. This behavior is not observed in 1.14.4 on the same system.
This bug appears to be operating system specific as it is not reproducible on Windows and only occurs on Linux as far as I am aware.
The attached video better shows this behavior and all F3 debug details.
Is this still an issue in the most recent versions (currently that is 1.16.3, or the latest pre-release 1.16.4-pre1) of Minecraft? If so, please update the affected versions and help us keeping this ticket updated from time to time. If you are the owner/reporter of this ticket, you can modify the affected version(s) yourself.