That was going to be my suggestion. A nice, tight, charcoal gray screen. I wouldn't even bother with removable. It should be permanant.

the bottom two windows on the balcony do not open. It's the windows above the silver bar that do. about 1 meter from the ground.

Could you show an example of what you mean, in terms of screen. Thanks for your help

Great view and whatever you think is secure, double it. Cats amazing little mischievous buggers.

Ditto to all above, screens do fail, personally I would never let my cats out on that balcony, I have a screened in porch on the ground floor, I won't even take a shower without bringing them in and closing the door. As the old saying goes"Doo Doo happens"

Cats aren't suicidal or stupid. I don't think I'd worry about it.

Thanks for the comments. Still looking for a solution with some examples if possible.

Here I am posting 2 videos to explain further

https://ash213.wistia.com/medias/2xjc4m4su2

and

https://ash213.wistia.com/medias/tvu4hsauvx

Thanks again

Since the garden area windows are remotely controlled, I still think screens will work the best. The frame could be made in a color to match your windows.

For the window, I couldn't tell how the hardware works as the window opens, but I wonder if you could place a screw/bolt/wedge somewhere along the mechanism to prevent it from fully opening. It could be a permanet placement or maybe something you insert each time you open the window.

Is there any chance a gust of window would close that window?

Joseph, you're correct that cats aren't suicidal or stupid, but when they become obsessed with a flying insect or a toy they lose all sense of location and danger. Many a cat has gone sailing off a balcony chasing a butterfly or bird.

I’m with Joseph , what are the odds?

I would want screens just to keep bugs out!
No, not suicidal or stupid but.....

I must say, that is a spectacular view! I understand you don't want to spoil the view with some sort of screen "contraption."

How about call a screen company or two to see if they can come up with something for you.

What about fishing net? Cover all the windows with fishing net. I found this photo online.

I once had the same problem; my balcony off the bedroom had a waist-high half-wall, and was completely open above that. I hired a carpenter who built a frame of 2x4's enclosing the open area, and nailed window screen to the frame. It worked great. My cats never damaged the screen, but some bird broke into an upper corner!

Since cats do like to perch on a window sill and watch whatever is happening outside, I would recommend you work a few nice sitting spots for your cat into your plan. P.S. When I moved out, I removed the whole balcony screen and frame. Good luck on your project!

Indeed, cats are very smart, but...they can lose all their intelligence when intent on chasing a passing bird or bug. A lot of cat fatalities have occurred by cats following potential prey out into space, then downwards to great injury. I like the suggestions of getting some sturdy custom screen panels. That's a beautiful balcony, but you are absolutely correct that your cats could find a way out and to great harm. Better safe than sorry!

My kitty Zizu caused my breathing to cease for a moment when she blithely walked right through the vertical bars on my balcony railing and went strolling up and down the rail-less edge, then casually walked back to safety. I don't think 30 seconds elapsed after that before I had ordered some vinyl-coated 1/2" hardware cloth online and installed it the minute it arrived with cable ties. All is safe again in balcony-land!