Hi Julio,
Have a look in /etc/apache2/mods-enabled/
. Make sure you enable the correct PHP version in apache, available versions should be visible in /etc/apache2/mods-available/
. To enable the corrrect version use the a2enmod
command.
Afterwards restart your apache with systemctl restart apache2
.
Please be aware that ownCloud only supports PHP 7.3 with the upcoming version 10.3.
Cheers,
Erik