h2testw, F3 and FakeFlashTest keep coming up as recommended for this.

Came here to advise running F3 to test the sd card, and make sure it’s legit.

Turns out the Steam Deck does it on it’s own when you use the steam UI formatter, Beautiful

Yes, there is one called F3 (Fight Flash Fraud).

Luckily my brother took care of that part. I just had to remember:

d:
cd games
cd cannon
[Space][Space][F3]

To play Cannon Fodder.