This Seeking Tech guide will explain how you can force Clair Obscur: Expedition 33 to manually save.
In order to do so, you need to take the following steps:
Use the following video as a visual aide:
1. Open the Expedition Menu.
2. Select Any Character.
3. Unequip and then re-equip any weapon, pictos or luminas.
4. Back Out of the Expedition Menu. The game should now auto-save.
The save file should appear at the top of the Load Previous Saves menu.