when copying banners you can put other items in and it will still let you copy the banner and will delete the other items. it is still in the latest snapshot.
Environment
server, singleplayer, and LAN. Survival, creative, and adventure. No mods, datapacks, or plug-ins. And with mods. Tested them all. May be possible in other versions.
Hey there!
This looks to be a duplicate of MC-170443.