Error message «This operation is forbidden»

Nextcloud version (eg, 10.0.2): 12.0.0.29
Operating system and version (eg, Ubuntu 16.04): debian jessie
Apache or nginx version (eg, Apache 2.4.25): apache 2.4.10
PHP version (eg, 5.6): 7.0
Is this the first time you’ve seen this error?: yes, first install

Can you reliably replicate it? (If so, please outline steps): yes, it appears everytime

The issue you are facing:
When I go to my default folder after first install (index.php/apps/files/), I have this error message.
I checked /var/log/apache2 log, they are empty…

I’m stuck, where can I look to have information about this message or how can I solve this?

Thanks

The output of your Nextcloud log in Admin > Logging:
No server logs
Everything is working fine

The output of your Apache/nginx/system log in /var/log/____:
none

I finally corrected the problem with an vhost apache config as explained Here

I just put Satisfy Any in vhost file .conf