Is it ever possible for a disk/volume to be mounted anywhere other than in /Volumes? It seems that under macOS that all disks of every type will always be mounted under /Volumes. (Except, of course, for the boot drive which will always be mounted at /.)
But is this just the case under &quot;normal&quot; circumstances for most people most of the time?
Is it ever possible that some kind of storage could be mounted elsewhere like on other *nix type OSes?
Sure - use the mount command by hand using a command line shell and terminal application.

Here’s how to mount a SMB share manually.
Here’s how to mount a AFP share manually.

Interrupting a direct attached disk mount is not as easy. (or documented here yet AFAIK)