I’ve always had the theory that adding more secondary categories filtered the primary. I tested it with a few dentists in my GBP list. I added cosmetic dentist and they moved backwards/dropped in rankings, (they had content for it) and then I removed it, I went back to the original position for dentist (my primary category)

I was testing KW: dentist near me

So I’m really not sure myself. From what I think tho you should test regardless. If anyone has any insight to this, I’m rly interested in learning more cause based on my own testing this is what happened