The solution to this is really pretty straightforward. I have a kitchen bay window overlooking a patio, and have several bird feeders at the edges of the patio. I used to get about a bird a week colliding into the center window (the 2 side windows of the bay window have screens, the center one doesn't). The last straw was several years ago when a hummingbird hit the center window with a
VERY loud THUMP! I rushed outside and the hummingbird was frantically flapping its wings beneath the window. I rushed into my garage to grab a shovel and gave it a mercy killing.
That was very hard to do.
Afterwards I scoured the internet and found the product below. I ordered a pane of it custom cut to fit that window. This was about 5 years ago. I haven't had a single bird collision at that window since.
https://www.collidescape.org/white
One side benefit is, I used to scare the birds away from my feeders when I went to look out that window. Now they (usually) don't see me and I can watch them at my feeders just feet away without scaring them.
The only issue with this is, you'd need to have, like, every glass high-rise in every big city to be installed with these things in order to do any good. A window here and there is nice but doesn't make much difference in the grand scheme of things. It would have to be installed everywhere.
I suppose you could start by requiring it on new construction, and then gradually make older buildings install it over some decades.
Also, encouraging or even requiring buildings to turn as many lights off at night during migration season would help.
EDIT: Also, since this product screens out a lot of sunlight, especially on south-facing windows, it would also cut down on air conditioning costs.