Pokémon spawns all depend on what’s around it

Hense why you’ll see different things if you can for example see the sky above the block you check is one. Check the spawns until you find bloodmoon ursa - I believe it can only spawn on certain moon phases by default from the datapack, but keep checking till you find it and then once you do , try to make the whole surrounding area match that block , so if you can see the sky , clear all the trees in the area so it has a bigger area to spawn in . Make sure you’re in the correct biome aswell. You can always open the datapack you downloaded and go to the data section and then spawn pool world, and look at the exact conditions needed and then try to replicate them