Information

Minecraft version: 1.21.4
Modloader: Fabric
Fabric loader version: 0.16.10
Environment: Singleplayer

Mod name: Smaller Nether Portals
Mod version: 3.9

Description

I created a regular nether portal in the overworld and went through, then went back and changed the overworld portal to a 2x2. I relit the overworld portal and went through just fine, and I changed the nether side of the portal to a 2x2. However, when I used flint and steel, it just lit a fire in the portal and didn't activate it.

Okay I should've probably tested a bit more before saying portals only work in the overworld.

I made a new portal in the Nether a few blocks away from the first one, this time sized 1x2, and it worked fine, so the bug is more likely that you can't reshape portals to be smaller when they were auto-generated by an overworld portal.