This just started happening recently. The attached video is of what I am experiencing. It happens in both Singleplayer and Multiplayer worlds. And has only affected 1.16+, whether it is vanilla, or modded like Optifine or Forge. While playing 1.8.9, and 1.12.2, this doesn't happen. Nothing has changed on my system to cause this so I am clueless on what is happening.
Edit 1: When restarting Minecraft and even my computer the bug still persists.
Edit 2: Even after re-installing Minecraft the bug still persists.
Edit 3: I figured out why this was happening! My Pen Tablet drivers were freaking out, and once i closed them i issue stopped.
I think you ou should try reloading Minecraft, then it may work.