So basically I was playing 20w21a with my friends (server hosted by one of us)

and we got to the ender dragon, we killed him and there was no end gateway to get to the end cities.

We searched for it even on spectator, even behind the island (just in case) but nope, there was no gateway

We respawned the ender dragon to see if this way we could get a gateway, but it didn't work either, we had to put it with creative mode.