Dear Aternos Team,
I would like to request a mod called Double Slabs.
Now, I have seen this mod requested before. However, I do not think the person making the request was describing the mod in its entirety.
Double Slabs is a mod that allows you to place two different slabs together, in one block. This is currently the only Feature, but there is plans for more.
There is also mod support.
Link: https://www.curseforge.com/minecraft/mc-mods/double-slabs
I hope you see this, and hopefully you add it.