@Alice595 A couple years ago Airbnb brought in a list of "essential" items that all listings must provide. Stuff like toilet paper, soap, bedding and towels. There was a huge outcry from hosts in places where linens and towels aren't traditionally provided, and guests who go to those places don't expect them. These were mostly hosts, as far as I could tell, who had beach vacation rental cottages on the east coast of the US, and some like that in Europe. They said their places were remote, that there were no laundry facilities, and no linen services, the hosts lived sometimes hours away, and that if they had to stock a place with enough sheets and towels for the 10 guests their places accommodates, and then find a way to get all that laundry washed, they would have to up the price of their listings to an absurd amount. Most of their guests drive in, so can easily bring their own bedding and towels.
Airbnb backtracked on that requirement because of the uproar it caused (wish they'd do that with profile photos!).
I would suspect that's what that Linen fee is about- for hosts who don't normally provide that, but will at an additional cost for guests who request it.