Given space limitations on both sides of window & the fan window above, the only idea that comes to mind is an at ceiling height mounted black out roller shade - maybe a decorative Roman shade type. It should extend past the window to corner of wall & same amount on crib sideboard prevent light seepage at sides.. The big deal will be to not have a cord anywhere near crib so maybe a motorized shade or if cost prohibitive then cord must be on wall side & length must be somehow controlled or cord must be mounted or secured to wall in case baby is ever playing in this room & could potentially reach cord.

Another thought - rearrange room to create space on left of window. Then mount drape pole at ceiling height & when open have drapery panel stack completely off window at left. Again, secure any cords for safety.

I’d just close the blinds during nap time and let baby learn to sleep in any light condition. Makes going places and traveling easier if baby doesn’t need complete darkness to sleep. Not being critical- I did this and now my daughter does same.

I do see blinds advertised as room darkening but don’t know much about them.

You could also have a decorative half-circle panel made for top of window above blind and hang short room darkening curtains that the rod is just attached to window frame.

Darker rooms promote better sleep for everyone. Babies also get better quality sleep when they're not moving around. You do you, mama, and if you want blackout curtains, go for it. You will need to rearrange your furniture, though. Not sure why you have a pack and play and a crib in there but if you add curtains you'll want them out of baby's reach (same with that name banner). Maybe swap your crib & changing table. Back to your question - we mounted a curtain rod wall-to-wall to cover up the wall behind our TV. Yes, you need to remove the decorative end, but your baby won't care. Place the rod halfway between the top of the curved window & your ceiling (or higher if your curtains are longer) and leave off the decorative end. Agree with pulling the curtains off to the left side so you don't block light when they're open.