Okay so "something" happened "some time" ago. A bunch of games stopped working including, but not limited to:
- Absolute Drift ZE (Steam)(32Bit / Unity 4)
- Assault Android Cactus+ (Steam)(64Bit / Unity 5/2017?)
- Bud Spencer & Terrence Hill: Slaps & Beans (Steam)(32Bit / Unity 5)
- Cayne (gog)(64Bit / Unity 5)
- Dex (Steam)(32Bit / Unity 5)
- Distance (Steam)(32Bit / Unity 5)
- Drunken Robot Pornography (Steam)(32Bit / Unity 4)
- Enter the Gungeon (Steam)(64Bit / Unity 5/2017?)
- Halcyon 6: LE (Steam)(64Bit / Unity 2017)
- Hollow Knight (gog)(64Bit / Unity 5/2017?)
- Jotun (Steam & gog)(64Bit / Unity 5)
- Layers of Fear (Steam)(64Bit / Unity 5)
- Shadowrun Returns (Steam & gog)(32Bit / Unity 4)
- Shadowrun: Dragonfall DC (Steam & gog)(32Bit / Unity 4)
- Shadowrun: Hong Kong DE (Steam & gog)(32Bit / Unity 4)
- Sundered EE (Steam & gog)(64Bit / Unity 5)
- ...and a couple more
This is the output of launching Cayne (which is free of charge on gog) from commandline:
Set current directory to /home/user/Games/Linux/GOG/CAYNE/game
Found path: /home/user/Games/Linux/GOG/CAYNE/game/cayne.x86_64
Mono path[0] = '/home/user/Games/Linux/GOG/CAYNE/game/cayne_Data/Managed'
Mono path[1] = '/home/user/Games/Linux/GOG/CAYNE/game/cayne_Data/Mono'
Mono config path = '/home/user/Games/Linux/GOG/CAYNE/game/cayne_Data/Mono/etc'
Native stacktrace:
[1] 10682 segmentation fault (core dumped) ./cayne.x86_64
As they all fail to launch with a segfault, I guess I'm missing a package or two which makes it a little more obvious as it doesn't matter if it's 32/64Bit or limited to a specific Unity Engine version.
For reference here's my inxi: Pow's inxi
...and my installed packages: packages.txt / GitHub gist
I also went through the process of trying all currently available nVidia driver versions being 430xx/435xx/440xx.
Any pointers or instructions for digging deeper welcome! 
