This is probably not what you’re looking for, but when I had a baby and was desperate for his nap times to last, I had to figure out a true blackout option for his room that had an odd shaped window. I bought white blackout fabric (available by the yard), a grommet kit, and suction cups that had a stem the size of the grommet holes. I cut the fabric slightly larger than the window glass, installed grommets along the top, and stuck the suction cups into each grommet. This lived in a drawer. When I wanted to black out the room, I stuck it to the window. (It took seconds). When I didn’t want the room dark, the whole thing went away and I had a nice window to look out.

I’m sure someone else will have a more elegant approach, but this worked. Sorry I don’t have any photos.

Thankyou! Practical indeed...

Hi. Lovely view. Maybe swing arm rods like these?