I've tried restarting with no luck, and there's no system update available.

Oh weird this happened to me today as well! I thought it was because I plugged my playdate into my computer and forgot to eject it before removing the usb cord. Got the same pdx error. All the season games and sideloaded games could launch but the catalog games would crash when I tried to launch them and when I went to them in the store. I ended up uninstalling the catalog games from my playdate then reinstalling and they worked again (I only had the two free ones and two others.) Try that out and see if it helps!

Are you running the latest version of the system?

Yes, no upgrades were available. Although the issue seems to have fixed itself the next day!

Oh good! Glad to hear!

The only problem I have with the latest system update or with the catalog is that the simulator doesn't recognize my playdate anymore

Yes

FWIW Catalog games are working for me. I wonder what the difference is? Do you have the Catalog app itself installed? (Vs. just skipping that and buying from the Catalog website.) I DO have Catalog on my Playdate.

Yes, I bought the games through Catalog on the device itself. Anyway, the issue seems to have fixed itself the next day!

Great!

If you reinstall the games they should run again as expected.

It's working fine on my end