3rd times a charm. THIS time, I choose "Allow all users" rather than just my specific user. THEN I increased the memory in the Cloudron app dashboard to 2GB, AND I edited the php.ini to reflect the same, then restarted. AND instead of just writing mysql in the db location I typed mysql:3306. So which ensured it worked this time? Who knows.
SPOKE TOO SOON. I had forgotten to edit the admin user fields, and pressed Install. It alerted me to this... but continued with the install! So I filled in the fields even though the spinning activity wheel was present (Chrome on a Mac). A few minutes later, as I was logged in somehow and editing the details for my company, it all crashed with a note about a fatal db error. I will try ONE MORE TIME, and if it still doesn't work, I'm turning my back on this infernal app.