Rotties living with cats are fine tbh, I’ve owned one, and fostered one and I have cats, I’ve know lots more that also live with cats well.
i will caveat that as if they’ve lived with cats as a puppy and their cats only - introducing an adult to a cat when it’s never met one rarely works and they can be overly interested in strange cats outside.
They’re great dogs but IMO much higher energy than most people assume they are - a step down from collies or spaniels, but not couch potatoes by any means.
A decent breeder with working line rotties wouldn’t sell to a pet home anyway, they’d be looking for them to be doing a sport so with show line it’s more goofy playful high energy than very driven, but they do need decent walks and a fair amount of other entertainment.
Theyre very enthusiastic about everything, so they’re great fun, but also they’ll do everything full on, even stuff you don’t want them to.
Theyre also more like a herding breed than lots of people think they are, fairly high prey/chase drive, easily overly stimulated in busy environments.
Youll find lots of stuff online with outdated training advice about having to be an alpha etc, because they do seem to attract that sort of person but actually they’re quite sensitive and do not respond well to harsh training methods.
They have absolutely no clue how big they are and think they fit on laps and want to, will just run straight into you because their brakes fail.
They’re an absolute dream to teach things to, you can teach them a new command reliably in one or two sessions and that’s it, they know it… but stopping self rewarding unwanted behaviours is much harder than in a more biddable breed.
They can be real chewy as puppies, complete dickheads as teenagers and because there a large breed it can be a good 3 years before they’re semi sensible adults.
They are a bit more prone to same sex dog aggression than some breeds and it can be a big downside for some people but people can be very weird about them as in you might find some people are iffy about their children being in your house with one. I once got someone asking me to move my dog so he could get past on the pavement… the dog was on a short lead, in a sit next to me hadn’t even looked round at the man about 8 feet from the gate the man was coming out of and the car he went into was in line with the gate - but apparently he needed more than 8 ft to get past the sitting dog on the 2ft lead 😐😂
It’s also quite hard to find a decent breeder, there are loads of shitty breeders, very few who test hips, elbows and heart and will weed out allergies, bone cancer and behavioural issues from their breeding dogs.