Bought this game, installed it and ran it with default settings, my monitor changes to a black screen, then goes back to Windows.
any idea how to fix this? if not, can I get a refund?

my system:

Intel Core i9 9900KF
Nvidia Geforce RTX 3080
16GB RAM
Windows 10 version 21H2

What screen resolution are you trying to use to play this game?
Fyi from what I've tested the game works up to FHD resolution. The QHD+ resolutions don't work and you have to use dxWrapper for that.

Hi. I tried anything as low as 640x480 but nothing works.

It's gonna be hard to diagnose what your problem could be without any logs.
Can you maybe follow instruction from this page https://github.com/Jones3D-The-Infernal-Engine/Documentation/blob/main/pre-mod.md#ii-set-the-game-starting-in-devmode to get dev window opened.
Than try to run game in window and set the `Error Output` to `Log file` and `Debug Output` to `Verbose`.
If the game still doesn't run in window mode paste the log file here and I'll try to see what the problem is.