It is probably either TomTom or Cartographer_Waypoints, though there might be other mods that look similar.
In the ss, the arrow used might be for QuestHelper (I don't know if other quest mods make use of a wp arrow but I know QH does). I don't know if it requires Cart_WP though as I had both installed to begin with.
Thanks for that, as it may prove useful to others. I use Bartender4 and it dawned on me that the thin border was likely just a tweaked DreamLayout, so I made my own ButtonFacade plugin that is just a slightly adjusted copy of the BF DreamLayout. It works nicely. :)