Please try the following troubleshooting steps:
1.) Double check how much free space you have.
Please make sure that your device's free space meets the required amount listed on our official website. In addition, the amount of memory space the game requires may increase with future updates, so please make sure you have enough ample space.
Required Free Space:
・iOS: 30 GB or more
・PC (Steam/Google Play Games): 70 GB or more.
2.) [Steam] [Steam Deck] Try changing the save location for the game files.
For PC:
Changing the game's installation location may help resolve the issue. For more details, please refer to the following Steam Support page:
https://help.steampowered.com/en/faqs/view/4BD4-4528-6B2E-8327
When choosing the file format for the destination drive, please make sure to choose NTFS.
For Steam Deck:
If the game files are saved in a microSD card, moving them to the device's internal storage may help resolve the issue. For more details, please refer to the following Steam Support page:
https://help.steampowered.com/en/faqs/view/69E3-14AF-9764-4C28
3.) [Steam Deck] Please update Persona5: The Phantom X to the latest version from your library.
Note:
・We cannot provide assistance for changing the game's installation location or updating the game. If you require assistance with those, please contact Steam Support instead.
・Changing these settings may cause unexpected issues to arise. Please proceed at your own risk.