Many players seem to wonder how they can save or quicksave in Assassin's Creed: Origins, and the answer is that it's simply not possible to do so. The game features autosaves only, so it is currently impossible to manually save.
The game autosaves very often tough, so it's always safe to turn of your game when you are finished. Every time you loot something, or does anything interesting, the game will automatically save.
If you really want to force a save tough, the simplest way to do is is to use a fast travel to another location. The game will always save when you arrive it this new location, so this way you can be 100 % sure that the game saved right before you turned it off.