Recently while visiting a family member in the hospital I noticed the curtain between the two beds was some sort of really effective sound blocking fabric. It also absorbed conversation on the side we were on which felt strange. It killed practically all reflected sound even with a wall of windows right there.
Custom Window Sound Blockers
I was today years old when I realized they made press-in sound blocking solutions for windows. I have never heard them so I need a well-heeled guinea pig from A'gon to please try them out and report back.