You can create a new exit end portal by upgrading a world during the dragon fight

Steps to Reproduce:
1) Open 1.19.4 and enter the end
2) Run /fill -50 255 -50 50 255 50 obsidian
3) Update to 1.20.1
5) Kill the dragon
6) Notice that the dragon's end portal has spawned at the very top of the world placed with the fill command.

Notes:
The old 1.19.4 end portal can not be used to respawn the dragon but the new one can.

Video