Windows 7 64 bit, gtx970.

I try starting rct1 and it goes to fulscreen, I can see my cursor and hear the game but get a black screen with a tiny pixelated mess box in the left upper corner of the screen.
Clicking where the menu buttons are seems to freeze the game/open the menu but I can't tell since I am working blind.

Compatibility mode doesn't fix this.
I suspect this happens thanks to the default fullscreen, is there any way to force the game to run in windowed mode without having to use the in-game menu?

Not only do you need compatibility mode, but you also need to disable Aero in the game's Compatibility properties.

Disable visual themes, desktop composition and scaling is ticked by default and changes nothing.

Solution found here:
https://www.gog.com/forum/rollercoaster_tycoon_series/rct1_deluxe_not_working_black_screen_top_left_corner_small_box
Go to the nvidia control panel, 3d settings under global and disable everything dsr.

Why is something like that not pinned?