If you break a decorated pot in a "hall" room of a trial chamber it wouldn't stack with normal decorated pots in your inventory.
Steps to reproduce:
Create a new world with update 1.21 experiment enabled
Set your gamemode to survival mode and difficulty to peaceful.
Give yourself less than a stack of decorated pots
Locate a trial chamber "hall" room
Break decorated pots found in that room.
Notice that broken pots don't stack with normal decorated pots in your inventory
Can confirm in 1.20.70.24 Preview, although it's a possible duplicate of MCPE-177064 since the NBT data carried by the decorated pots dropped are the reason why it's unstackable with normal decorated pots.