I personally would not want a view onto a four season porch, which oftentimes can get cluttered. Maybe consider clerestory windows in that space. It would allow some light into your living area but not a view. Either that or just sheet rock it closed and try to maximize lightening up the room in other ways.

https://www.google.com/search?q=clerestory+windows&client=safari&hl=en&prmd=isbvn&sxsrf=ALiCzsa0wc9YKdHjEl18eGKITzJDkQ_rpA:1660495579185&source=lnms&tbm=isch&sa=X&ved=2ahUKEwiQwZeJ5Mb5AhW1GDQIHQTmDaUQ_AUoAXoECAIQAQ&biw=375&bih=553&dpr=2

Can you show the rest of the room? Where is the entrance to the sunroom?

Depending on your style, filling in the window opening with another window you like will let in the needed light and control the porch climate.

Personally, I would look into a custom made Black steel room divider, with 'window panes' filled in with glass or not.

Any welder can create a framework with style and have a building contractor install as you would a window in the opening.

I'd leave it open through the fall and winter. Then you will know if you need a new glass window there for warmth or if you can simply frame it with wood trim like the other windows. You can get a quote online for a new window and an estimate of the delivery time.

I don't think the opening is too big...as you say, it brings great light. Replace is with another window and treat it as such:

Why not do a transom window. Letting in light, but cutting out the view of a room that

appears not to be fully utilized.

I'd make the porch an extension of the living room. Improve the flow to it.

My first inclination was a double French door, until I realized you have another door as an entrance. Maybe a French door look, but with windows, like in New Orleans.

If the four season porch stays at the same temps as the living room, I would just open a doorway between the two spaces. How could we help you rearrange the furniture for that?