I checked the update logs, In 1.21.0 They added it as a "fix" where the GUI does close every time it is cloned, because i guess it crashed peoples games when it stayed open, so I'm just going to put it in the minecraft feedback site. Everyone who is on this post can try to vote for it though so we can hopefully TRY to get it back in the game.
RegentStew42092
I checked the update logs, In 1.21.0 They added it as a "fix" where the GUI does close every time it is cloned, because i guess it crashed peoples games when it stayed open, so I'm just going to put it in the minecraft feedback site. Everyone who is on this post can try to vote for it though so we can hopefully TRY to get it back in the game.