The gateway does not appear after killing the ender dragon. Even after doing it twice. I am playing on vanilla 1.16.1
Linked issues
Comments

the world was opened on a snapshot, but the end was only created on 1.16.1

Please read the moderator note on MC-184482, and in the future, please be more vigilant when using early development previews of the game.
Did you open this world in any 1.16 snapshots?