I found these files that would result in a big dump that probably isn’t pertinent.
/usr/share/applications/org.kde.smb4k.desktop
/usr/share/plasma/plasmoids/org.kde.smb4kqml/metadata.desktop
But “.desktop” rang my bell. I should have tried new users before posting. For them the icon shows up in menus. That narrows it down a bit.
Solved. A while back, once I got Smb4k working with /mnt/smb4k as its mount point, I inadvertently left it set to the default /home/user/smb4k. Once it was changed back to /mnt/smb4k and /home/user/smb4k was deleted, the icon started showing up in menus. Favorites is favored again!
Was this a case of what you were referring to here? If I not I suppose two different mount directories conflicted.