Solution:
thanks to Marting.B posting his Apache logs - yeah I should have though of that earlier - I checked mine and found " Could not initialize a database connection: could not find driver" .
I then found the following article https://github.com/NagVis/nagvis/issues/119
This showed that I needed to add a missing dependency “php7.0-sqlite3” I didn’t have “php-sqlite3” loaded so I didn’t need to uninstall it
then I needed to enable the extension in “/etc/php/7.4/apache2/php.ini”
uncomment “extension=pdo_sqlite”
then restart the apache server and all worked
so I fixed my issue by
sudo apt-get install php7.0-sqlite3
sudo vi /etc/php/7.4/apache2/php.ini <== uncomment (line 935: extension=pdo_sqlite)
sudo systemctl restart apache2.service
SO I hope this helps if someone else has the same issue