

While experimenting with screen resolutions to solve the fullscreen issue, with some of them I was getting parallel lines displayed across the very first loading screen after launch and onwards, including actual gameplay sections. 1400x1050 didn't have this issue for me, but your mileage may vary.
If you're getting black screen after trying to initiate fullscreen, try experimenting with your desktop resolution. The game doesn't seem to like 16:9. What worked for me was 1400x1050. In my case, the game window is shifted downwards a bit (I can still see my desktop's top bar, and when there's more than three lines of text in the game's text box, only about 75-80% of the fourth line is visible).
Slight cursor desync that others have mentioned.
3w is enough to run the game

Used accesibility zoom at 1.70 factor without mouse tracking to have the game running in an almost fullscreen-sized window. Can be activated with 'meta'+'+' and reversed with 'meta'+'-'.
Fullscreen turned into a black screen.
Proton 6.10 GE
You need a little tweak to initiliaze full screen: 1- Open the game normally and enable full screen mode, the game might crash or a black screen might appear. 2- If the screen is black close the game. 3- Re-open the game, a black screen will appear. 4- Click super key and then come back to game. Now there shouldn't be any issues with fullscreen. (You need to this step everytime you open the game.)
If playing in windowed mode is fine then the game can be enjoyed.
making fullscreen would crash then game
Text speed becomes very slow after playing the game for sometime
The full screen issue required me to use a magnifying glass software
Full screen does not work, I had to keep the game windowed in its default resolution.
There were missing characters in notebook with proton 5, it was solved forcing the use of proton 4.11-13
If you're stucked with a broken full screen and alt+enter does not restore windowed mode, you can delete the datasc files, but it also includes save files.

I played the entire game with all the endings and did not encounter any breaking bug but after 25 minutes or so, the framerate start to plunge witch may be immediately perceptible if your text display setting is set fast enough. Restarting the game temporary fixes the issue but it will happen again 25 minutes later. Also as mentioned by someone else, the clue selection UI is slightly out of sync with the actual mouse position and pretty laggy overall.

Trying to run it in fullscreen can result in it crashing and then refusing to launch until you restore the configuration files datasc.ksd and datasu.ksd in savedata subfolder to their previous state. Also in the clue selection UI mouse selection position often desyncs from actual mouse position and there is some input lag when clicking. It's not too hard to deal with this however and the game is playable and completable.

Game runs fine - Tested both visual novel sections and investigation sections, as well as skip and autoread. No configuration required.
Game will boot and look normal (though there is an error-message window immediately). However, it is not possible to interact in any way.
Tried disabling Esync and D3d11 and using wine D3d11.