So after today's update and the addition of the snapshot 21w11a, I can't load my server which was left at 21w05b since all the latest snapshots cannot load old worlds.

I tried to load other versions and it seems to load just fine.

Please fix this as soon as possible I can't open my server anymore, or make it so we can play old worlds too in the new snapshots. Thanks!

Edit:

I tried to load 21w05a and it's also broken. But in this one at least it tries to load until it fails and shows the error "Sorry, unable to start Minecraft." at the top right corner, while in 21w05b it does nothing when hitting the Start button.