The duplication feature works with create contraptions unless items are in it, but it is possible to duplicate a large amount of blocks by putting them all in a contraption and then duplicating the cart item. I would suggest preventing the duplication of contraptions.

can you give me the id of that item? should be added to the blacklist

create:minecart_contraption

So the mod scans the item nbt to try to figure out if it has items (god have mercy this won't work as well anymore on 1.21). This means that somehow it still doesn't detect that item. Can you send me it's nbt? Get it with command

Still works on 1.21, here have its data, might be a better idea to add create:minecart_contraption to the blacklist

hmi was sure it was added

i can do better and blacklist its component type