I think bathroom fans are common enough, we did a trip to Northumberland last month and the rental house had fans, exhausting to the outside, in all 3 bathrooms plus the kitchen.
I think mold is becoming more common since the subsidy driven push to insulate houses this last 10 years. The rental house we moved into when we first moved back in 2016 had mold in the bedroom and entrance hall, and our landlord, who lived in the street behind, said that his father-in-law, who had owned the house, had cavity wall insulation plus so much extra loft insulation that you can't see where the rafters are.
Our good friends in the town have been in the same situation so this summer had ridge ventilation tiles installed, plus we saw another house a few weeks ago having ventilation tiles installed.