My mobs aren't spawning in my dimensions.

When I downloaded 2020.3 version, all of my custom mobs have vanished. And I've read the "bugfix #xyz", but what if I don't want to turn on the global light source and I don't want to make the basic blocks to grass material. And if I'll set the mobs from creatures to mobs, then they'll spawn absolutely nowhere. (I mean, they only spawn in the overworld(Which I've enabled to)) So, this is the problem.