For nodebb I got:
[harderer@andromeda ~]$ ll /var/www/ | grep nodebb
drwxr-xr-x. 12 harderer harderer 4096 Apr 17 19:15 nodebb
And I followed this official nodebb guide for installation. Maybe I should add, that I use nginx as a proxy to Apache?
And no problem for going on, thanks a lot already for looking into it! 
Edit: This is my current nginx config:
upstream forum {
server 127.0.0.1:4567;
}
server {
listen 80;
listen [::]:80;
server_name forum.******.de www.forum.******.de;
return 301 https://$host$request_uri;
}
server {
listen 443 ssl;
listen [::]:443 ssl;
server_name forum.******.de www.forum.******.de;
ssl_certificate /etc/letsencrypt/live/forum.******.de/fullchain.pem;
ssl_trusted_certificate /etc/letsencrypt/live/forum.******.de/fullchain.pem;
ssl_certificate_key /etc/letsencrypt/live/forum.******.de/privkey.pem;
ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
# disables all weak ciphers
ssl_ciphers 'AES128+EECDH:AES128+EDH';
ssl_prefer_server_ciphers on;
location /.well-known/ {
allow all;
}
location / {
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
proxy_set_header Host $http_host;
proxy_set_header X-NginX-Proxy true;
proxy_pass http://127.0.0.1:4567;
}
location /socket.io/ {
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
proxy_set_header Host $http_host;
proxy_set_header X-NginX-Proxy false;
proxy_pass http://forum;
proxy_redirect off;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";
}
}