When I press "Load" or "Save", it shows this error:

Wait Until DataReady!

I can't do Any% because of this. Can't save or load my progress

Also I want to ask where are the Legacy and the new version? I can only find one version of the game

Legacy doenst exist anymore and the point of legacy was that you could load saves so you cant load saves anymore

Then why are the save and load button still there?

probably because the game uses an outdated data store service no real way to know though tbh someone can definitely remake the game if they want to, as dex should work for getting the obby itself