I've been using Photoshop CC on my Macbook Air for a while now. My system is a 2017 Air running Big Sur (11.3.1). up until today I've had minimal issue setting my WD external hard drive as my scratch disk. Today it just wouldn't show up in my options for selecting a scratch disk - and because my computer is running really low on space (<3G), I can't open PS to troubleshoot from the inside. I've reset the settings using Shift+Command+Option, and I've checked that my external is running MacOS extended (journal), and it still won't work. I'm a bit at wits end over here - any help would be greatly appreciated!