Are you sure it’s cats?

Have you seen the cats pooping or just sniffing the poop?

Depends where you are, but foxes would be a more likely bet. Fox poop stinks too - really foul stuff. Cat poop generally is quite inocuos once it drys out, although a lawn mowing bot slicing it up would make sense for making it worse.

I have never heard of cats pooping in the middle of a lawn before. Normally they like private and safe spaces to poop as they’re vulnerable when pooping, and normally they’re fastidious about burying it where possible.

iF it really is cats, then maybe get a gravel section next to your lawn that they might prefer to go in? A litter box essentially.