I am running 1.16.4 on MultiMC with Fabric and Optifine installed. I made sure that Immersive portals was working by just testing it with Optifine running and it worked fine. As soon as I enabled DoorsOfInfinity, my log was flooded with "[main/WARN]: Received invalid biome id: -1" I don't know what could be causing this because I don't know anything that would be conflicting with this mod, but yeah. This is my TedTalk lol

Also getting this issue. Has nothing to do with Optifabric.
The game becomes pretty unresponsive, basically frozen, although every so often I can hear the animals around me. Unfortunately, waiting for this causes the log to generate a ridiculous amount of entries. MultiMC stops displaying the new entries but says it probably hasn't stopped making them.
It looks like the dimension is in fact created, but something else goes wrong.