Version Information

Forge version: 30.0.43
Botania version: 1.16.5-419

Mobs can spawn on abstruse platforms, which was not possible in 1.12. To make sure that this was true, I loaded up a 1.12 superflat and made a basic spawn platform and made a roof to lower the light level to zero to allow mobs to spawn on the platforms; Nothing spawned on the platforms at all so I can confirm that not allowing mobspawns is an intended mechanic of the block. Also, the abstruse platforms allow light through which is also an intended mechanic and present in 1.12, so it doesn't make sense to allow mobs to spawn in the first place.