The page # in the margin is dependent on the format of the books being read. If it's a standard ePub then yes, there is an option to remove the display of page #.
If on the other hand it is a kepub, either straight from Kobo via WiFi or Desktop, or via the enhanced Kobo Driver in calibre, then there is not a # in the margin; rather, it's at the bottom of the screen.
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