"Craft isn't installed yet" error after updating to Craft 3.1 I just updated to Craft 3.1 and logged into the admin to make the required updates to the database and this all worked fine. However, when I use the new ./craft update CLI feature, it responds with "Craft isn't installed yet", even though it's on a year old Craft project and just successfully updated to Craft 3.1?

There's not really any other messages to go on for this one. See below.
Have you tried running ./craft setup to double check if your setup is correct? 

If ./craft setup completes successfully ./craft should find the existing installation and complete any required setup. 

In my experience, this is usually related to a non-default /config/db.php or problematic .env file.

Note: Always do a backup before trying anything related to setup just to be on the safe side.