Arched windows are decorative and let lots of light come into your room. But for some people it’s difficult to find treatments for them, as it’s difficult to find bay window curtains. But many sites offer arch window blinds, fixed and movable. Arch window blinds are easily operated from the ground or can have motorized mechanisms. For example, Bali has 1/2" aluminum blinds for arched windows, stationary pleated shades for quarter/half-circle, full-circle and non-perfect arches, and more.
Hunter Douglas has movable wood and fabric arch window blinds: An almost invisible string goes from arch rail to arch trim through the blind; you operate these arch window blinds with a sliding handle. They have inside mount and different opacities.