Pigs will not spawn in plains if Environmental and Geckolib are installed. If another mod using geckolib as a dependency adds a mob to another biome in which pigs spawn, the pigs will not spawn there either.

Not an incompatibility, environmental reworks farm animal spawns - replace this biome modifier to undo this: https://github.com/team-abnormals/environmental/blob/1.20.x/src/generated/resources/data/environmental/forge/biome_modifier/remove_spawn/pig.json