Our office has 3 walls made of glass

There are no blinds/curtains/etc

Every day, between about 1pm and 4pm, they Destroyer of Eyeballs hangs in the sky above my monitor, before it finally gets blocked out by another tower block

I now time-track 3hrs less each day - eventually someone will realise that buying blinds is cheaper than paying me to not work 15hrs/week

That's just so...stupid.

Get a VR headset.

The best part is that people will think you ski a lot. It will look like a ski goggles sun tan.

Damn, not I want an HTV Vive Pro.

I think you should get a bunch of Post-it notes in as many colors as you can find and start tracking the sun across the windows in a nice and orderly fashion.

Then you can explain your productivity loss with Post-its being the biggest thing you could find that sticks, so blocking the sun is a tedious process:
1. Enjoy a few seconds of focused work
2. Get hit by sun
3. Locate precisely where sun is
4. Get up and place Post-it in the exact location
5. Sit at desk and go to step [1]

In the end you'll have a mural of colors streching across the suns varying paths or recognition that it might be a good idea to order some blinds :)

Similar situation at a client in Dallas. I moved one of the giant rolling whiteboards in front of my desk and used some jb weld to render it immovable. Thanks to the laziness of their office staff, there it remains each time I have to fly in.

Purple spraypaint works pretty well on glass. Well, the color doesn't actually matter but purple is nice.

That is just illegal in my country