My world has recently reached a size of 1GB. Previously, I could duplicate it thanks to the Copy World button (I create backups regularly) but since it is 1GB it does not work anymore.
The error message is: "You are almost out of data storage space! Minecraft has restricted access to this feature until you clear up additional storage space." which makes no sense because I have hundreds of GB available on my disk.
Copying other (smaller) worlds still work fine.
It's not a big deal because I can of course duplicate the 1GB world directory on the disk myself, but doing it in game thanks to this button was convenient.
Either this is a bug, or if the limitation is intentional for whatever reason, the error message should be modified to explain that large worlds cannot be copied with this button.