In Bedrock 1.21.51, the problem has been fixed by replacing the new Edit World Screen introduced in Bedrock 1.20.60 with the older version of the Edit World Screen.
If the 1.20.60 Edit World Screen is enabled again later, this problem could reappear.
Tested on iOS 18.1.1.
In Bedrock 1.21.51 the problem now occurs when duplicating worlds with names 28 characters or longer, now that the newer 1.20.60 Edit World Screen has been re-enabled, and world names have been limited to 30 characters.
Tested on iPadOS 18.1.1.