Can't load singleplayer world after 20w21a

I didn't use this world since 20w18a, so I've checked every new snapshot:

20w18a: yes

20w19a: yes

20w20a: yes

20w20b: yes

20w21a: no

20w22a: no

I did use the "Create backup and load" button instead of the "I know what I'm doing!" button.

When it finished the backup it loaded from 0 to 100 instantly and then it just freezes. I noticed my cursor had the loading animation just before loading the world.

I even tried to Optimize the world + Erase cached data on both versions but the only thing that changed was that it didn't go from 0 to 100 instantly anymore..