I think some sort of trellis on the side facing your next door neighbor with some climbing vines/flowers is your best bet.

Forgot to mention that it gets pretty windy where we are. Not going to be able to maintain plants.

Have a simple glass window made for the space. Use frosted glass.

If you can't maintain a real plant, giant faux fern hanging (fern is appropriate for that light). This one is huge but you can get smaller depending on your measurements. It blocks their view without being obviously unneighborly. Not sure why you can't maintain one more plant when you have this lovely garden, though?

Switch it out in the winter for something holiday decor. (assorted hanging snowflakes/kissing balls/windchimes/moroccan lanterns/flags etc).

If you don’t want curtains and it’s too windy for plants, I think windows may not be an option. You could try privacy screens, but that’s very similar to lattice. If you have the boards slanted correctly, they let the right amount of light in and help with the wind. Or you could just get to know your neighbors better. :)

In my experience, curtains aren’t particularly prone to damage (get panels made from outdoor fabrics), but there are other options...

Install stainless steel eye hooks and run stainless steel wires through them to create a sturdy trellis. You have a vine growing in the front, so you should be able to find a vine which can stand up to the wind and climb the trellis.

Home Depot has nice panels on their website similar to this that aren't the standard square or diamond lattice.

We are lucky the plants just grow here with a drip installed and only need a trim every few months. No water set up for vine and don’t want the extra maintenance. But agree those look nice. Thanks for the great ideas.