I buy flea traps that have a sticky pad under a night light. It catches tons of them if they are around. I also use food grade diatomaceous earth under the furniture. I think you can apply it directly to a cat like flea powder but make sure it’s food grade. It’s not a poison. The little sharp pieces cut into the flea exoskeleton and kill it. We have never had them like we did last summer. So far the Seresto collars (the real ones) work great on my house dogs and haven’t caused any reaction. I need to get out in their yard and powder it too because now is when they should start emerging.
We had a billion fleas due to skunks living under the house. I mean billions. Skunk fleas don’t live on cats but jump on, bite, and jump off. We used DE for the cats, also fed and got rid of a tapeworm btw. We used those flea catchers with a light but it didn’t get near enough, so we put DE in the house and outside where you could practically see the ground moving. (no grass, just dirt and oak leaves). The final coup de grace was when DH went over the ground with a propane torch...
Been there, done that with the diatomaceous earth, I buy it by the 10 lb bag for internal consumption (cats and humans), but it has done little to nothing when applied directly to the cats - other than piss them off and create lots of dust. Fleas don’t seem to mind it.
Instead of buying the flea traps w/night light, I just use pans of soapy water with a light hanging over it - same idea, and yes, it drowns any fleas who jump toward the light.
But they say that for all of the fleas you manage to catch, it’s only the tip of the iceberg, and I believe it!