I was using an older version of OSMC, pre the big SMB security update, with my Macintosh OS X 10.8.5 system. I was able to browse to and mount the SMB shares from my Macintosh.
I have now upgraded my Macintosh to OS X 10.12.6. I am still sharing files using SMB. The OSMC on my Raspberry Pi 3, hardwired ethernet connection, computer was no longer able to access the shares. The only thing that changed was the Mac OS.
To try to solve the problem I upgraded the OSMC to the latest version, OSMC 2018.1-1, Kodi 17.6.
I can still airplay to the Raspberry Pi so there is a connection between the devices.
In particular. I’m trying to add a video source under video>Files. I choose SMB. I choose to browse. WORKGROUP appears and I choose it. iMac appears (name of my Macintosh). I choose it. The wheel spins a bit and I get a dialog saying: “Operation Not Permitted”.
I also find that the OSMC does not appear when I browse the network for shares. An old Raspberry Pi 2 running OpenELEC does appear when I browse for it.
It would seem like there is an issue with respect to both the newer Mac OS and the newer OSMC.