Minecraft v1.15.2

Currently Double Slabs from that mod cannot be used.
Would this be possible to support?

Do you mean support for camouflage, or does it not work as the elevator platform?

Yes, the slab blocks do indeed have tile entities.

currently I don't allow blocks with tile entities for the platform. I will probably change that in the future, but it will be a while before that happens.

It doesn't work as a platform, although I hadn't tried the camouflage

Oh ok, well camouflage shouldn't work as that only works with full blocks.
I will look into why it doesn't work with slabs, it is supposed to work if the top of the block space is solid, thus it should work when the top slab is there.

Maybe the Double Slabs mod has them as tile entities?

Oh well then that would be the reason, currently I don't allow blocks with tile entities for the platform. I will probably change that in the future, but it will be a while before that happens.