Tools like DepotDownloader (GitHub) can automate fetching older builds if you own the game legally.
If you still have the Steam license and want a clean pull: Mafia 3 Downgrade 1.09
If you want to hunt the cult in Sign of the Times or drive the Samson Harrier in Faster, Baby! , . The DLCs require patch 1.11 or higher. Mafia 3 Downgrade 1.09