Animal Mobs not spawning

I am aware that this topic has been discussed before, but I've tried all of the solutions given from the other discussions I've found and nothing seems to work. Vanilla animal mobs won't spawn in my custom biome/on the custom grass blocks i have set for it despite me trying to use dirt/grass tags, setting the material type as grass, trying to use the validspawn tag, and trying to set them to spawn with a different spawn type (monster/ambient, etc.) and its really frustrating. The version I'm making the mod for is 1.16.5 so I'm wondering if theres something specific I have to do for that game version