Are Steam games kind of sandboxed?

[Markus Schaaf]

Hi all,

I am trying to access a folder directly beneath the root folder 
of my computer from inside a game (Symphony), using Steam Linux 
Runtime (no Windows emulation like Proton). Strangely that 
particular folder is missing (some others like /boot and /opt 
too). Then there is a folder /overrides that does not exist in /. 
So this is some kind of sandbox, but I have no idea where to 
look, if I want to whitelist or link other folders there. Can 
anybody help?

BR
Markus