Ice & Fire is heavily modified in ATM 1.16 based modpacks.
I&F Dragons only spawn in "The Other", a custom dimension you can reach by using a teleport pad in the Nether. (Shift-right click with an empty hand, and nothing in offhand)
Travel 800 blocks from spawn in The Other, and look for specific dragons in specific biomes.
Natures compass and spectral eye amulet will help. There is also a scrying ritual from Ars Nouveau that can locate chests.
Higher tier dragons are in underground roosts around y35.
Right click with an empty hand to loot a dead dragon.
Note: Loot with a bottle in your hand to get dragon blood. This will change the loot table so you only get bones, blood and skulls.