I don't know what is the host system on these ready to use microSD, but it should usually be a Linux anyway.
Sheepshaver (like BasiliskII) usually can mount a shared folder called "Unix" from the host on the MacOS desktop.
It's an handy way to share files, if your host is reachable from your network of course.
You can define that shared folder in the SheepShaver preference file that is in your host user home folder,
it's called ".sheepshaver_prefs" (the dot makes it invisible in files browsers...).
you can open it with any editor, like: nano .sheepshaver_prefs
and check if there is a line starting with :
extfs
if not, just add a new line in that pref file like so :
extfs /home/YourUserName/
Then your host user home folder should mount on the MacOS desktop as "Unix" folder next time you start Sheepshaver.
About using USB ports in SheepShaver, some infos :
There is a precompiled BasiliskII in RetroPi according to this thread :
But didn't tried it myself.
I've built my own using this guide :
That's really helpful - many thanks!!!!