When i set the flat world as "air" and i create this world, i am not in the middle of stone platform.
MC-190374
Player does not spawn in the center of the void stone platform
Open
6
(Unassigned)
Confirmed
World generation
air, cobblestone, flat, flat-world, middle, stone, stone-platform
1.15.2, 1.16 Release Candidate 1, 1.16, 1.16.2, 1.16.3, ..., 1.18, 1.18.2, 1.20.5, 1.21.1, 24w35a
Retrieved
Every world has a 21x21 block-area where the player can spawn if no bed/respawn anchor is found, so probably this is intended.