Custom Roman shades with black out lining..

Here you go:

ANGLED AND SPECIALTY SHAPED WINDOW COVERINGS · More Info

Read the article attached to this picture.

Houssaon's pic is what came to mind. I would not call that complete black out, however. Do they come in black and if they do who REALLY wants that? The only other thought were the blinds inside the window panes but getting all new glass would be super expensive. It sort of appears that is an upstairs window so the designer must have thought privacy was not a need? I would be tempted to make that a room where the windows were free to be unadorned.

https://www.amazon.com/Natural-Silk-Sleep-Mask-Blindfold/dp/B01ILWXKS2/ref=pd_lpo_vtph_121_tr_img_2?_encoding=UTF8&psc=1&refRID=QSPGHNSNFD8Q38SZRYMY&dpID=31FSUf%252BDvYL&preST=SY300_QL70&dpSrc=detail

^Consider an alternative answer to window treatments. Consider a sleep mask rather than window coverings. This solves the issue without ruining the beauty of the windows. I would leave them without any window treatment at all. Maybe film to reduce the glare. It looks like you have privacy already with just a tree view.