Starting from 0.9.7 BetterEnd mod required dependency
BCLib : https://www.curseforge.com/minecraft/mc-mods/bclib
But it's not added to Aternos yet
I tried to suggest it but it just said it's not popular enough
However, BCLib already had 5000+ downloads
BetterEnd already had latest update on Aternos but since BCLib isn't added yet we can't actually use it