

There is cross-platform play between PC (including Linux and Mac) and mobile devices (iOS and Android). For other platforms like Nintendo Switch and Xbox, crossplay is not available, meaning you can only play with others on the same console
You should be able to play co-op across PCs regardless of OS but console versions are not cross compatible.
Density and cultural norms in general are definitely a factor.
If I was out and about in my normal area where I live in the US and someone got close enough to pick my pocket I’d be on high alert because they are way inside the normal personal space bubble here.