I have built a creeper farm using this design: https://www.youtube.com/watch?v=_Yv74wRjrR8
In vanilla 1.16.1, creeper behaviour is as intended. Creepers run from the cats and plummet to their doom. They see the trapdoors as a safe space (even though it isn't).
However, in spigot 1.16.1, the creepers run to the edge of the platform and stop. After a while they may wander aimlessly until they either fall, get pushed off or despawn.
It's worth noting that when on the ground and placing a cat in front of a creeper, the creeper will path find away from it. So behaviour in this sense is correct.
Applying the glow affect to the creepers at the farm, I can detect between 16 and 40 creepers on the platforms at any one time in spigot 1.16.1 and thy can remain there for quite some time. In vanilla 1.16.1, the creepers are on the platforms for 1-4 seconds before running away from the cats.
Also worth nothing that, generally, I've noticed the creepers huddle on the edge of the platforms. Almost as if they are aware of the cat but cannot run off the edge of the platform because they do not detect the trapdoor as a safe space (the behaviour which is expected, is that they do detect the trapdoor as safe to walk on, as per vanilla)