I propose that certain Better Spawner Categories count as certain regions when it comes to breeding. Categories that are similar to the region should count as the region. As long as the ranch block is in the biome, the two Pokemon inside the ranch are considered to be in the corresponding region when it comes to breeding. For example, breeding a Rattata while the ranch block is in a biome that counts as Alola would result in an Alolan Rattata unless the regular Rattata parent is holding an Everstone.
Here are my suggestions:
- Alola - Beaches category
- Galar - Taigas category
- Hisui - Mountainous Forests category
Maybe there are better categories that fit the regions, but those are the best that I can come up with at the moment. If matching Better Spawner Categories to regions causes problems (such as conflict when biomes are in multiple categories), then individual biomes could be matched to the regions instead. In that case, the Beach biome can be Alola, the Taiga biome can be Galar, and the Wooded Mountains biome can be Hisui.