Problem With Biomes

I am using version 1.16.5.

I have a problem where my biome won't generate my custom trees on my custom grass. The grass is set to grass material and my trees are set to 14 per chunk. Once I set my biome to spawn normal grass, my trees generated. Also, my biome wont spawn gravel patches when they are set to spawn 4 per chunk. Lastly, I can't get anything to spawn in my biome, I set slimes to spawn with a weight of 15, min group size to 1, and max group size to 15, however, nothing spawns.