I have been trying to make a modpack to play with friends. I thought it would be really cool if there was compatibility between Dragon's Scourge effect and Ice and Fire. I tried looking through configs yet I haven't been able to find a way to do this.

Yes there is! I mentioned it in the changelog when adding the effect, but essentially it checks for all entities inside the "dragons.json" entity type tag. Just make a datapack where you add the ids of the dragons to it, you can find it data/forge/tags/entity_types/dragons.json (it is inside the generated folder here on github in the forge branch).

Thank you so much for helping and answering so quickly.

No problem. I am going to add Ice and Fire to the tag by default next update, was planning on doing it when adding it but must've forgot.