From what I understand about fire ants, you have to kill the queen to destroy the colony. Just killing a bunch of ants accomplishes nothing. Same thing with termites.
I personally like Orthene from the box stores.
https://www.lowes.com/pd/ORTHO-Orthene-12-oz-Fire-Ant-Killer/5013597781
It's a very fine white powder that you just barely sprinkle on the mound. They say the best time is early morning or late evening, when the ants are most active. But it really doesn't seem to matter when you do it, the mound is always dead the next day. The biggest issue with Orthene is the smell. It's horrible!!!!
Usually I do my walk through the yard the day after I mow it. I just deal with areas that I keep mowed. When I see a mound forming, I sprinkle a little Orthene it and it's done. The bright white color of the powder makes it easy to see what mounds I've treated and what mounds are new. Usually in the Spring, there are a lot of them, but by Summer, there will only be a few of them. By the end of Summer, it's rare to see any new mounds.
My wife is finishing up the Master Gardener program with Texas A&M, and they recommend sprinkling Diatomaceous Earth on the mounds. I haven't done that yet, but plan on giving it a try in the Spring when the mounds start to show up.
When I've been bit by fire ants, I've found that for me, Hand Sanitizer works great. I think the alcohol dries out the bite, and that stops the inflammation. I used it during Covid because that's all I had at the time, and I was surprised by the results.