I am unable to get to Hades #9 after competing Hades #8, Persephone's Mansion.
Looked in Olympus on the main map?
I have no idea how to get to Mount Olympus!?!? Main map!?!?! The game has always taken me to Mount Olympus...
pixel_player586077871 Main map is a term used for the desktop version, ignore that.
For mobile, just scroll to the extreme left of the Greece map and you'll see "Olympus" among those mines.
This guide has some images too on where to find - https://www.diggysguide.com/guides/finding-new-quests