it errors out with "cannot create subdirectory in temporary directory"
What OS are you playing on? Which folder did you unzip the game into?
Win 10 1809. I let the Itch.io client handle the install, it has the sandbox turned on. So, it goes under Appdata/roaming/itch/apps/
Ah, went to the folder and the exe launched fine. So Itch’s attempt to launch as a constrained user is at fault?
That's probably it. Darn, I wonder what I could do about this...