My grandparents home built in early 1900’s & a Sears kit home, had a small transom high in wall between kitchen & bedroom on other side of wall. The opening was @ 12” x10” or so - much smaller than your opening. It had a small door matching molding etc & was opened by rods that pushed it out at angle & rods could be reached when standing on floor. Purpose was to allow heat into room from kitchen wood stove. Bedroom had a window. Could you put glass, either decorative or plain, into the opening to provide sound barrier for rooms on both sides of window & then also install a pleated blind on inside of window on bedroom side to allow light to pass through? If emergency exit access needed through window, then maybe a sliding window - no screens of course - would work.

ETA - it seems to me a treatment that provides privacy but that also retains this historical feature would be a win-win.

Even with modern HVAC, you still need air to circulate. There probably isn't a return duct in that room. If you could do a transom window like KW describes that would be ideal since that is probably how this worked originally.

Are you sure it was originally a bedroom?

Another thought - what about installing white, inside mounted shutters or louvers of some kind? Not sure how effective a sound barrier that would be but the long louvers would look ’right’ in the opening, not be airtight as a solid glass window so though airflow wouild be restricted when they’re closed some flow would be allowed. Maybe even just inside mount wooden blinds? Lots of options for light & air with raising, lowering, closing completely etc.

I would add a movable transom window. It could be done in leaded glass if that suits the home's style, or you could have a custom stained glass panel for it. Maybe your daughter and you could get your heads around designing a piece. Here are some inspopix.

https://www.houzz.com/photos/query/stained-glass-transom-window/nqrwns/p/20?oq=stained%20glass%20transom%20window&redirectoq=stained%20glass%20transom%20window