NC 11.0.3 -- PHP7 -- occ

Hi,
I am trying to use occ to install the server software on the RaspPi of a Nextcloud Box.
When I start occ the following message is returned

PHP Warning: PHP Startup: Unable to load dynamic library ‘/usr/lib/php/20151012/mysqli.so’ - /usr/lib/php/20151012/mysqli.so: undefined symbol: mysqlnd_connect in Unknown on line 0
PHP Warning: Module ‘mysqlnd’ already loaded in Unknown on line 0
PHP Warning: Module ‘PDO’ already loaded in Unknown on line 0
PHP Warning: Module ‘mysqli’ already loaded in Unknown on line 0
Nextcloud is not installed - only a limited number of commands are available
No database drivers (sqlite, mysql, or postgresql) installed.

An unhandled exception has been thrown:
Exception: Environment not properly prepared. in /var/www/nextcloud/lib/private/Console/Application.php:144
Stack trace:
#0 /var/www/nextcloud/console.php(89): OC\Console \Application->loadCommands(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#1 /var/www/nextcloud/occ(11): require_once(’/var/www/nextcl…’)
#2 {main}

As can be seen, mysqli is looking for a mysqlnd symbol even though mysqlnd was loaded.
According to the PHP website mysqlnd has been removed since PHP5 and it is recommended to use mysqli instead.

Is this a problem of occ or of PHP?
Or do I have a competely different problem?

Thanks in advance for your help.

K.D.J.