The Bug

I am on a vanilla installation of 1.16.3 and made a nether portal. On one end, nothing is changed, but the other is blocked off from both sides. When entering the portal from the normal side, you get trapped in the other. You can still open the pause menu but not the chat so it is impossible to, say. call for help if you're on  server or /home. Also, since I dont have a pickaxe, the only way out is to break an obsidian block with my unaided hands, as you must re-enter the portal to trigger it to the other side. This was tested on a vanilla single player world.

Reproduce

• Build a Nether Portal
• Go through it
• Block both sides with obsidian
• Go back to the overworld
• Go back into the nether with the portal built earlier

Observed Result

You were trapped in the portal

Expected Result

You wouldn't be trapped