Plesk CLI commands do not work when logged in as the root user on Debian 10

Symptoms

Trying to use any Plesk CLI commands when logged in as root on Debian 10 fails:

# root@server:/home/jdoe# plesk -v
bash: plesk: command not found

Cause

Even though the superuser rights have been granted for the current user, it is still not root - it can be confirmed with the following command:

# root@server:/home/jdoe# echo $USER
jdoe

Resolution

Log in as root using the following command:

# su -