In servers, when your setting blocks to end gateways/portals at a certain scale, w/ the setblock command or MCedit/WorldEdit, There is a Mass reduction of FPS (like 0.2) and there is a 6 sec delay after you press esc for the pause menu to show up.
Please make a way to remove end portals/gateways in creative on a large scale.
new world generation is not in 1.17, but 1.18