I was in a house that had full blackout treatment which was blinds that set into a track on each side of the windows with a box valance above. 100% blackout for a bedroom that faced a streetlight. If you don't need 100% black out. use blackout curtains that mount close to the ceiling and go all the way to the floor and are wider than the windows on each side.

Thanks for your suggestion

The solution I used in my family room was dark grey velvety ish blackout drapes hung with a blackout rod. This rod curves at the ends, jutting out about 4 inches from the wall. This allows the drapes to hug the wall completely as they go around the curve. I’m not explaining it well, I’m sure. But I got both items on Wayfair or Overstock or similar. You can probably google “ blackout curtain rods”. The rods are heavy duty because the curtains are lined and heavy. A really cheap way is to use black stick on accordion paper blinds from Amazon. I used those as temporary and they blackout out very well. Ugly as sin, but they work for under $40.