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As far as I know, in 21w06a update, you are forced to reset the world because of the new cave generation and extend world height limit. Maybe wait for a new update come, then you can update it.
i was thinking that as well as it wont le you do it in single player worlds either (i checked after)
I have a server where i update it for every new snapshot but with the newest 21w06a snapshot it wont let me update it. it asks me to reinstall the server which will delete everything. is there a way to update from 21w05b to 21w06a or is it because of the big world generation changes?
