I'm also affected this bug in 1.16.3-forge-34.1.42.
I can suggest two workarounds.
A. Downgrade version of forge. 1.16.3-forge-34.1.35 works fine.
B. Try to remove OptiFine_1.16.3_HD_U_G4 and restart. ( In my case, OptiFine was the only one that was installed. )