Is my SD LCD screen busted?

After a system patch last friday, my SD's screen now stays black, but it still works fine when I connect it to an external monitor through USB-C>HDMI.

When connected to the external screen, I can run and play games just fine, and even the SD's touch screen still work properly.

I've re-imaged my SD, as described on Steam Deck Recovery Instructions, so now my SD is completely 'fresh', but that didn't change about my situation. I've opened up the case, as suggested on ifixit to see whether anything was damaged or loose, but nothing seemed out of the ordinary.

Short of replacing the entire screen or motherboard, does anyone have tips on what else to try?