I know this issue was supposed to be solved but in my survival world, which I created in 20w21a, the End Gateway that is supposed to take you to the outer islands still doesn't generate for me.
I have respawned the Ender Dragon at least 5 times now, I've even clicked the optimize world option, everything. No Gateways though. I built a 1000 block long bridge to the outer islands, and the Gateways that take you back to the main island generate there, though.
I don't understand why the Gateways on the main island never generate when I beat the Ender Dragon...
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Duplicate of MC-184482, please note that if the end was opened in either 20w20a, 20w20b or 20w21a, no end gateway will be able to spawn.
Use an NBT editor like NBTexplorer and delete the DIM1 folder. Also go to the level.dat and go the the dragonFight section and add the entries for the gateways.