When installing Yunohost for the first time on Debian, the installer message says
Your configuration files for : … nginx … will be overwritten !
But the file /etc/nginx/nginx.conf is not overwritten.
The Debian was not a fresh install and the nginx.conf file content was in conflict with the yunohost installation. [FAIL] Installation of Yunohost packages failed
Removing the custom file in nginx.conf solved the issue.
This issue is minor and easily fixable but could happen to someone else so I report it here.