1. Create a datapack
2. Add a loot table (datapack/dragonmounts/loot_tables/entities/dragon.json)
3. The loot table doesn't apply, can be called with /loot give @s loot command but not /loot give @s kill which means it's not bound to the entitiy

Also tried with other paths and specifying the type which doesn't work either

Yeah.. this is an oversight on my part. The base dragon looks for a loot table based on its breed rather than the dragon itself.

Not sure how to approach a solution here; so far I have
"Try breed loot table if it exists otherwise default to entity loot table"

Overall an oversight on the fact that the base mod does not provide a loot table.

Thanks for reporting.

Is there any way to at least specify a loot table for one of the breeds or is the mod coded in a way that it has no way of altering the loot table? Or i'm not even sure if forge creates an empty loot table for every single defined mob, but then it's just the path that's nowhere to be seen, can't even find it in the mod source code.

For example i'm trying to make an end variant drop a head and an elytra which can be combined with a crystal to craft a new egg and revive them, although i can't just make a function that does /execute as @e[type=dragonmounts:dragon,nbt={DeathTime:1s}] because @e doesn't select dying entities