Ah, thanks, I searched for the recipe but all I could find is "4 pottery shards." I tried several arrangements but I guess I missed that one!
can confirm what PvP Panda says, if you dig around in the room you will expose a set of stairs. follow stairs to bottom and turn towards the center of the room. be careful though, because if you let sus sand fall, it breaks the contents.
can also confirm this is still an issue in 1.18.2
specifically for me it was unpowered repeaters on top of barrels and command blocks
Ahh good to know! I wonder if future snapshots/updates will have a more intuitive way of placing an item in the sus sand in creative?