Custom world generation or dimensions from data packs don't work in Java Realms

Hi,

One of my friends tried to load a datapack using custom world generation onto a Realm. This datapack (incendium-v1.5.zip) worked completely fine in single player, but on a Realm it appears to completely break the Nether and End. The datapack in question does not affect the End at all, it only modifies the Nether.

 

Here is a link to the affected world.

https://drive.google.com/file/d/1frwH3vF0DdpbJq7Xc4X_oEY36A2_nVvh/view?usp=sharing