So I'm trying to be able to Alt+Tab and running the game from Gothic.exe doesn't do it... and apparently it doesn't come with a fullscreen borderless windowed mode (which someone forgot to mention when I saw the tip)... oh, also every time I change the resolution it does nothing and changes back anyway.

GOG installs a fix that prevents Alt+Tab to avoid potential stability issues. Go to Programs and Features (appwiz.cpl) and remove GOG.com Gothic 2. You'll then need to install the Gothic and Gothic II fullscreen border fix to get the borderless capability back again. Windowed mode is set in GOTHIC.INI in the system folder where the game is installed.

As for the resolution you need to press Enter to confirm the resolution change in-game; if your resolution isn't listed in-game you can set that in GOTHIC.INI as well.

Don't Alt+Tab during FMV cutscenes or loading screens as this will probably crash the game (which is what GOG wanted to prevent).