On a specific SINGLEPLAYER superflat preset, it said "Server Closed" on singleplayer.

Reproduction Steps
1. Go on super flat and put this in the generation code:

2;7,50x1,2x3,2;2;stronghold(count=20 distance=1 spread=20),biome_1(distance=9),village(distance=9),decoration,dungeon,lake,mineshaft(chance=0.23),lava_lake

with the seed being -1910616783936951309

2. Generate, wait, and it will say "Server Closed."

3. It brings you to the multiplayer menu.