Can fly in survival with elytra in the overworld and nether just fine, but not in the End.
(Unwanted) new feature or bug?
(This has nothing to do with unloaded/new chunks, as it was tested several times in the same world, on the main island.)
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migrated
It had NOTHING to do with unloaded chunks, because everything was loaded. Don't know why you stitch them up as duplicates.
Oh well, you'll figure it out some day…