I also fixed a weird SteamDeck issue this week. Maybe others will run into it. My deck started going super slow, and having trouble booting. I even tried a factory reset to no avail and was getting ready to warranty it, when I thought to try one last trick.

Apparently going into the system setup menu (hold Volume + while turning it on) and turning on long term battery storage mode, then turning it off again (by booting up with the power cord in) somehow fixes this issue. So i did that, and it worked!

I’m mystified as to what random setting got flipped that this corrects, but I’m happy it worked.