Just fired up Voyager on Android to discover a notification-style marker above the settings/gear icon. Opening Settings doesn't provide any clue as to why. Taking it further by tapping each of the top level menu items also doesn't show why.
Okay, Voyager. Keep your secrets...
Edit: F-Droid showed that Voyager had recently updated, so I tapped the recent apps button and swiped up to close Voyager. When I reopened it, the marker was gone.
Weirdly mine seems to have disappeared without doing anything around the time I read this post...