Thanks, Justin. It doesn't appear to be a bookmark (and neither does the bottom one). This is the right-click menu:
To test further, I added another share through the file mgr. under "+Other Locations" (instead of adding it to fstab) and ended up with one entry:
I was able to add a bookmark to the new share:
The bookmark doesn't have the unmount ("eject") button next to the share name.
My end goal is to have a few shares auto mount, and hopefully see one entry per share. Is adding them to fstab still the best way to do this in Solus? Or should I be going about this a different way? Thanks again.