This Seeking Tech guide will explain how you can transfer your save progress from the PS4 demo version of Metaphor to the full version on the PS5.
For the first step, you need to download the full PS4 version and then open it. You then need to select the Yes option when asked if you want to fetch the save data from the PS4 demo version.
Afterwards, load into the save file you want to transfer over to the full PS5 version. You then need to manually save to the Network Data slot.
Next, you need to open the full PS5 version. When you select the Load Game option from the main menu, you should now be able to resume your progress from the PS4 demo version.