[Bug] Updating to 1.21 breaks previously made worlds (Temporary Fix Available!)

[Spike-has-no-idea-how-to-code]

What happened?

A bug happened! Worlds that were made pre-1.21 are broken after updating to that version. Entering dimensional portals is impossible even in creative mode. This is something definitely on your end, devs. Fortunately, all is not lost. You can fix this issue with minimal consequences by replacing the "level.dat" file in your world's folder with a level.dat from a world you create AFTER updating. This will cause your old world to change its in-game name to whatever you named the temporary world, but you can easily change that back in-game. Hope that this saves someone a headache or two, it sure did for me.
PS: I can't select 1.21 in the "What version of Minecraft is installed?" field.

BetterNether

Latest

BCLib

Latest

Fabric API

Latest

Fabric Loader

Latest

Minecraft

1.20.4

Relevant log output

No response

Other Mods

No response

[Spike-has-no-idea-how-to-code]

Edit: make sure to create a world with the same gamemode as whatever world you lost, I just realized that if you make a creative world it'll change the gamemode to that.
Edit to this edit: this is fake, it will say creative but it wont be. 💀