GoG homepage > (your name [drop down menu] when logged in) > “Games” > Click on any game in your collection > Download offline backup game installers
You can download installers for whatever systems the game supports – usually that’s just a Windows .EXE installer (+ several .bin files if the game is large). For games intended to run on Linux w/o WINE, you can select “Linux” from a drop down where it says system and it will give you an .sh file.
I set up a couple profiles with different colored backgrounds so that I can easily visually distinguish terminal windows when I have several open at once. For example, I usually switch the profile to one with a red background when I ssh into a server to help avoid confusion about which system I’m running commands on. I also cranked up the font size a bit in all profiles to make it easier for me to read.