Staredown: So if I'm understanding things properly, Caster of Magic is an expansion/proto-DLC/official Mod for Master of Magic which is included in Gog's windows install, but I do not see any mention of it for Linux. Is it there or is it only for Windows?
Everything that is for Windows, works normally for Linux, yet it is not mentioned, as no one is willing to support it.
While it's usually no-brainer to launch Windows games on Linux, sometimes they just get stuck and it takes luck and expertise to find a workaround.
https://imgur.com/R2hLnJ8 The bundle of GOG works fine on Linux, it even has GOLD level on Proton.
I was able to run Caster of Magic for Windows just fine.
Trying to run Caster of Magic would probably require me to implement DosBox instead Proton/Wine, but when CoM for Win works, no need to meddle.
It was just trying to install Gecko for random reason, not even sure if it needed or not.
BTW, I am using Heroic Game Launcher, also Lutris can be used, or a cheeky workaround by using Steam + "import non-Steam game" -> properties -> compatibility -> select any Proton or other Wine-like option.