I've had washer dryers ever since I got married, now on my fourth. We also have five cats so what I do is "de cat" the laundry before it goes in the wash. I use lint rollers to get as much of fluff and pet hair off the things to be washed.
It helps, I quite often put some white vinegar in the final rinse (doesn't scent the laundry) which also helps. Another thing to try is do a cleaning cycle, once a month run your washer with no laundry and put some washing soda crystals in the powder drawer and some vinegar in the rinse drawer, alternatively you could try one of the washer cleaners/sanitisers in the washer instead. An engineer who came to declare my last washer dryer was dead, told me that the soda crystals were probably better than a proprietary brand of washer cleaner.
That's all I can come up with, though I think it also depends on the brand of washer dryer you buy, I had an Electrolux which was awful, two Bosch, one of which I had for over ten years and no problems, second Bosch lasted four years
Just bought a Candy, so far so good.