Cannot edit or delete the world name. Only applies to the downloaded realm copy of the world, and does not affect my Switch or iPhone version of Minecraft, only my Windows version. This is the only version of the 3 I own that does not show the original world name and shows a different menu.
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The screenshot just shows the new create/edit world UI. What happens when you click in the box with the world name? Could you record a video of what happens when you try to edit the name?
I checked again and the issue seems to be fixed. It used to only affect long realm names, and now I am longer running into those issues with the same length names.