The iMac and MacMini are both connected to an AT&T 5286AC router via Ethernet and wifi. There are numerous other devices connected to the router via wifi (phones, iPad, Chromebooks, Windows laptop, smart home devices, etc.). I powered off the Windows laptop, reset the router, and shutdown and restarted iMac and MacMini. Doing this did not resolve the problem. If you want to pursue this, you could provide details on how to trace the SMB connection. I am UNIX literate and comfortable with a Terminal window.
I created this discussion, because of a concern that the Pages/Numbers/Keynote apps were incompatible between the iMac and MacMini environments. This is clearly not the case, since the iMac files open correctly on MacMini when transported via a thumb drive. So I don't have any further concerns and don't mind using the thumb drive solution. Note that file sharing of other file types (pdf, jpg) is successful.
Thx.