Cats do shit on concrete - sorry to disillusion all the cat lovers here. And cleaning themselves with their tongues does not make them hygienic.
We have a similar problem here. Our frontage is open concrete to allow for parking. Our back garden is lawned and enclosed to keep our dogs in and safe.
One of our opposite neighbours hasn't had her cats neutered so relies on Facebook posts to get rid of the kittens her cats are continually having. The kittens she doesn't find a home for she refuses to feed or allow in her home. She never flea treats, grooms or worms them either. She's one of these stupid people who thinks cats look after themselves apart from food. Her long-hairs look terrible with matted coats, the short-hairs do much better,
As a result, the batty old guy a few doors away feeds them outside so we now have a colony of well-fed but otherwise not looked after cats that are also breeding. The bird population has decreased locally but the rat population has grown and become bolder. We see them out in daylight now.
They're attracted to the food batty neighbour leaves out but are unchallenged by well-fed feral cats who would rather catch and play with small birds that live in the hedges in the street. One neighbour has Nest can footage of a feral leaping out of the hedge and catching a bird on a 5ft feeding station - that's now been moved.
Our concrete is used as a regular toilet by cats. Caught on our opposite neighbour's front Nest cam. I put pots out with flowers for the summer. Her camera also caught cats balancing on the rim having a shit. I was just about to plant a few more flowers in the pot when she ran out and showed my the clips on her phone.
I wear gloves to garden but there's nothing worse than getting your hands in cat shit. I have to wash the gloves off and bin them and they're not cheap.
We've tried all the deterrents like ultrasonic/flashing lights, citrus products and lion poo. They work for a while but the cats get bold. We had one cat owner complain about the noise of the ultrasonics!
The best deterrent so far has been an automatic water sprayer. Cat owner came over and threatened to report us to the police. We ignored her but only put it on on Saturday nights now as it caught our postman one morning. He was not amused but is on Team Dog (despite being bitten by a few - usually owned by "entitled idiots" - his words) and also has a similar cat-shitting everywhere problem.
The most depressing part for us has been the raised vegetable beds we put in. Raised and fenced to keep our dogs off but it doesn't stop the cats. We had to bin all the almost grown veg due to the cat shit the first year. That was an expensive and disappointing waste.
My sister has an indoor cat that is well-cared for. She has all her flea treatments, vaccinations and any other meds and is pampered royally. She's a happy little thing and doesn't miss the outdoors that she's never been in. Despite not going outdoors where she could pick up all sorts of crap, she's not allowed in the kitchen unless someone's in there as she tries to jump up on the worktops where she would leave germs from using her kitty litter. My sister always likens it to wiping your bum and then preparing food without washing our hands.
If all other lazy cat owners were like my sister the rest of us that have to put up with crap (literally and figuratively) would be a lot happier (and richer). Let's face it, a cat is the perfect pet for lazy and inconsiderate owners like the people in my street.