Recreating a void superflat world would cause the platform to not spawn. Just make a flat world using void preset, recreate it, and there won't be a platform.
Affected Things
Void Platform
Decoration (such as Grass in "Overworlds" preset)
MC-188491
Recreating a superflat world would cause certain things to never generate
Resolved
Awaiting Response
9
(Unassigned)
Confirmed
Normal
Custom Worlds, Structures, World generation
1.16 Pre-release 3, 1.16 Pre-release 4, 1.16 Pre-release 5, 1.16 Pre-release 8, 1.16 Release Candidate 1, ..., 20w46a, 20w48a, 20w49a, 1.16.5, 21w08b
Retrieved
In 20w29a.