Need to see the whole room and both windows to offer possible solutions. Post more pix, please.

It’s not allowing me to attach other photos.
The window on the other side of bed is like this one except the trim doesn’t terminate into a sloped ceiling. It’s a “normal” window, with 9 ft flat ceiling.

Add the pics in a comment . IMO yu can't hide that flaw so mjust use romans shades in a fabric that works with the bedding and your eye will go to the shade and not that awkward corner . I do agree we need to see the whole space too.

No biggie - think of it as being part of the charm of the house. You can install blinds that fit inside the window casing. Aren't there some there now? If they're not particularly lovely, just get something else more attractive.

If it were mine, I would play it up.

Paint the wall (behind the headboard) an accent color and paint the rest of the room & ceiling. white. I would hang inside mount roman blinds, AND a drape panel on the inside of both windows.