itch.io

I solved it btw,  I think. I saw the #1 game in art category of this jam, and it has exactly that. Not that simple on Unity, but...

You need to enable click to full-screen in game page on itch. That will enable full-screen right away, (well, you still have browser bar on top and windows bar at bottom, but still good, you can enter full full screen with F11) esc doesn't exit full-screen mode. And in Unity build settings there are 3 pre-made options templates for browser, we need 3rd, then it will stretch game to whole screen. A "little" problem: then you can resize browser window however you want, you can make it extremely horizontally stretched for example,  and be able to see beyond your intended screen boundaries.  And Unity doesn't have aspect ratio support as far as I know. So I needed to implement my own, so I can force game to run at 16:9 always,  with black bars. So it's a bit of a hustle but I was able to replicate the behavior of that #1 art game pretty close. I hasn't fixed yet my upload, but maybe I will. 

Upd: updated game, now esc doesn't exit fullscreen