Why some number updates shown as incompatible on my Mac

Thank you for your help. It tells me that my macOS High Sierra ver. 10:13:6 needs to be updated to latest version. How t that? My app store did not notify about updates beyond this version. It used to do earlier. I shall update it immediately. Guide me to how to do that now.

Hi! Dialabrain Thank you for your help. Now as I understood the next version of macOS Sierra 10:13 is mac OS Mojave and that will solve my problem. Is this correct understanding. If you say yes, that solve my problem

Thanks you and await for more clarity