Could not initialize Photoshop because the scratch disk are full

From the Adobe forum

Since you cannot start Photoshop, you cannot change the scratch disk allocation in its preferences. Luckily for you, the engineers have devised a shortcut to fix that: Hold down CTRL+ALT(PC) / CMD+OPTION(Mac) as soon as Photoshop starts to get this menu:

Select another disk with more room but do not forget the clean the files clogging up your hard drive, as described in the other messages.

Unfortunately, this didn't help me.

I had to clear out an extra several GBs and reset my Photoshop preferences. To clear the Photoshop preferences, you hold down Ctrl+Alt+ Shift (PC) or CMD+OPTION+SHIFT(Mac) as Photoshop is launching (just like you do for previous answer). This brings up a menu asking if you want to do clear the preferences.

I have had success in the past just deleting my preferences without clearing out memory, so that might be something you try. That said, you won't have your preferences, but that was minimal change for me. You can find more information at this Adobe Forum Question/Answer.

Afterwards (when Photoshop launched), I also increased the RAM for Photoshop.