Posting this hoping it saves people lots of trouble. I could not get rid of "$cfg['TempDir'] (/usr/local/CyberCP/public/phpmyadmin/tmp) is not accessible." Using Ubuntu 20.04.2 LTS.
I had this issue and it was mind numbing to figure out. I hope this saves folks trouble as it cost me hours.
Here is how I fixed it for me... edit the config file /usr/local/CyberCP/public/phpmyadmin/config.inc.php
I had to change:
$cfg['TempDir'] = 'tmp';
$cfg['TempDir'] = '/tmp/';
And that fixed the error for me on Ubuntu 20.04.2 LTS