Tread carefully... This course of action would almost certainly result in a S21/NTQ at LL earliest opportunity as you suggest, as it is very confrontational!
I am a landlord myself, as a family we own a few and over the course of letting them to various people its interesting to see the differences different tenants make. Families with the same number of people, first lot were in for ~2 years with zero issues, place was handed back with some wear and tear but nothing to heavy. Next lot in, same size family and they complain of damp within 3 months. Place was streaming, black mould forming everywhere etc.. They were drying clothes on radiators and not ventilating the place, and they had about twice as much stuff in the house (so everywhere was a bit jam packed, little room for air movement). Damp is 'usually' down to tenant lifestyle, and most people dont realise they are the cause of the problem.
Why not reach out to the landlord and ask them to visit if possible, run through the problem and see if they can advise on what T is doing wrong, and offer to assist with sorting a solution. As a LL we would rather have a good tenant in for a long time than ongoing chopping and changing.
Drimaster PIV works really really well, at refurb we are fitting them to each of our lets. the slight positive pressure forces air movement out of little gaps in the windows etc and really helps to dry things out. You have to see it to believe it! Doesnt cost much more than a dehumidifier and is cheaper to run.
Have a chat with the LL, you might find a good solution together.
