So it does now work. I had to combine the two .conf files to one and make a symbolic link from the /opt/… to /var/www/openproject. I used
sudo ln -s /opt/openproject/public /var/www/opp
to create the Link.
Now the only issue left is that the Document root is still accessible… i tried to use a .htaccess file to block this with a “deny All”, but this doesn’t change anything.
For futur references here is my resulting .conf:
Include /etc/openproject/addons/apache2/includes/server/*.conf
<VirtualHost *:80>
ServerName my.dyndns.com
RewriteEngine On
RewriteRule ^/?(.*) https://%{SERVER_NAME}:443/$1 [R,L]
Alias /nextcloud "/var/www/nextcloud/"
Alias /opp "/var/www/opp/"
<Directory "/var/www/nextcloud/">
Options +FollowSymlinks
AllowOverride All
<IfModule mod_dav.c>
Dav off
</IfModule>
Require all granted
SetEnv HOME /var/www/nextcloud
SetEnv HTTP_HOME /var/www/nextcloud
</Directory>
<Directory "/var/www/opp/">
Options +FollowSymlinks
AllowOverride All
<IfModule mod_dav.c>
Dav off
</IfModule>
Require all granted
SetEnv HOME /var/www/opp
SetEnv HTTP_HOME /var/www/opp
</Directory>
ErrorLog ${APACHE_LOG_DIR}/server13_error_log
CustomLog ${APACHE_LOG_DIR}/server13_access_log common
RewriteEngine on
RewriteCond %{SERVER_NAME} =my.dyndns.com
RewriteRule ^ https://%{SERVER_NAME}%{REQUEST_URI} [END,NE,R=permanent]
</VirtualHost>
<VirtualHost *:443>
ServerName my.dyndns.com
DocumentRoot /var/www/
#DocumentRoot /opt/openproject/public #original root
Alias /nextcloud "/var/www/nextcloud/"
Alias /opp "/var/www/opp/"
<Directory "/var/www/nextcloud/">
Options +FollowSymlinks
AllowOverride All
<IfModule mod_dav.c>
Dav off
</IfModule>
Require all granted
SetEnv HOME /var/www/nextcloud
SetEnv HTTP_HOME /var/www/nextcloud
</Directory>
<Directory "/var/www/opp/">
Options +FollowSymlinks
AllowOverride All
<IfModule mod_dav.c>
Dav off
</IfModule>
Require all granted
SetEnv HOME /var/www/opp
SetEnv HTTP_HOME /var/www/opp
</Directory>
ProxyRequests off
Include /etc/openproject/addons/apache2/includes/vhost/*.conf
SSLCertificateFile /etc/letsencrypt/live/my.dyndns.com/fullchain.pem
SSLCertificateKeyFile /etc/letsencrypt/live/my.dyndns.com/privkey.pem
Include /etc/letsencrypt/options-ssl-apache.conf
# Can't use Location block since it would overshadow all the other proxypass directives on CentOS
ProxyPass /opp/ http://127.0.0.1:6000/opp/ retry=0
ProxyPassReverse /opp/ http://127.0.0.1:6000/opp/
</VirtualHost>
Thank you all for helping me!