Windows OK - Android can't load games - Any suggestions?

[Firestorm962]

I have PPSSPP installed on my Windows PC where it works great.
However, my phone (S22 Ultra if it matters) installation is not able to load a game.

PPSSPP on the phone is the current version from the play store.
The windows version is 1.13.1.

I've tried 3 ISO files so far, all of which work on my windows install.
On the phone, the icons for all the games show up as a gray box with a white question mark in them. I get a message saying "Could not load game. Not a valid disc image." when I try to play the game.

I can copy the ISO files back to my PC where they work again (separate folder from the originals to make sure I was testing the right ones).

Out of curiosity, I tried a couple games from the homebrew store (Cave Story & Breakout) both give the message "Could not load game. Failed to read identification bytes:". Not concerned about homebrew functionality, just mentioning it in case it is related.

Any ideas or suggestions, or further information needed to make a suggestion?