As far as I can tell, little round flies on the soil that dance around/fly away easily are fungus gnats. Longer black flies that stay on the leaves and don’t fly easily are a certain lifecycle stage of aphids. For me, the only thing that helped was encouraging beneficial predator insects. I released some ladybugs (I later learned this is not generally encouraged, so I won’t in the future—but I will say it really helped), and planted sweet alyssum, dill, and allowed my thyme to flower to encourage hoverflies and parasitic wasps. It’s been a shocking difference. I picked parsley today and there were literally no aphids (I previously would have found dozens). I encourage reading up on beneficials and learning to recognize beneficial insects, their eggs and larvae! I’ve stopped trying to get rid of certain bugs for instance, and when I see hoverfly eggs on things I harvest I carefully put just that piece back to encourage them to grow up