First of all, check all your biomes you created inside of your dimension. On the 3rd page of the Biome, check "Entity Spawning Properties". Press clear. This will prevent mob spawning in this dimension completely and you can now customarily add the ones you want to spawn.
If you did that for all your biomes but the mobs still keep spawning, then go to the dimension you created. On page 2 check "Biomes in this dimension: Blocks and properties are inherented from them". If you have biomes from the overworld selected then that will also cause the overworld mobs to spawn as that is part of the "inherenting properties".
What biome types are registered in your dimension?
A custom one that I made, it's called "Rast"
Sorry, it is "Rast Dimension"
First of all, check all your biomes you created inside of your dimension. On the 3rd page of the Biome, check "Entity Spawning Properties". Press clear. This will prevent mob spawning in this dimension completely and you can now customarily add the ones you want to spawn.
If you did that for all your biomes but the mobs still keep spawning, then go to the dimension you created. On page 2 check "Biomes in this dimension: Blocks and properties are inherented from them". If you have biomes from the overworld selected then that will also cause the overworld mobs to spawn as that is part of the "inherenting properties".
Ok, I will check it out