Okay, with a 99% probability I simply cannot specify the syntax correctly, but it seems that the "moddedVillagerWhitelist" option does not work normally.
I'm trying to ennoble the guards from the guard-villagers mod
(as an example).
I tried to specify this mob in several options:
at first as

"moddedVillagerWhitelist": [
    "#guardvillagers:guard"
  ],

then

 "moddedVillagerWhitelist": [
    "guardvillagers:guard"
  ],

and finally

"moddedVillagerWhitelist": [
    "guardvillagers.guard"
  ],

After each change in the configs, I first tried to update the guards on the existing map through the command, and then created a new map and checked it the same way on it. But squidwardism is incurable.
Please tell me what I'm doing wrong.

Entities needs to extend from villager so convert, but guards are technically not villagers. I added more explanation to the config wiki page. Realistically, that config option is quite useless, its only used in rare examples where a mod extends from villager, but only adds neglectable features (animations, custom model, ...) but is otherwise convertable to a vanilla/mca one.