Nginx + gitlab-workhorse doesn't work properly

Hello everyone,
the last time I tried to get gitlab to work, I didn’t make it - I switched to the docker container.
This time I wanted to make it work without the docker and I overcame several “problems” - if I understand it correctly, the only thing I still have to get working is the interaction with nginx.

I use nginx on port 80 for “normal” http requests, and on another port I want to be forwarded directly to Gitlab. I don’t want to use an SSL certificate, so I want to access Gitlab via http if possible.

Gitlab-workhorse is configured and runs on port 8080. If I want to use e.g. port 81 on nginx now, I would have to “take over” the forwarding to 8080 via a second HTTP block in nginx.conf (at least that’s my thought). I get an error message from my browser (google-chrome, same on firefox) when accessing gitlab over nginx via 81, that a secure connection can’t be established, although I deliberately choose not to use HTTPS.

The question is: Am I doing something wrong or is there no way to access Gitlab without HTTPS only via HTTP via NGINX?

Systemd parameters gitlab-workhorse:
ExecStart=/usr/bin/gitlab-workhorse -listenUmask 0 -listenNetwork unix -listenAddr /run/gitlab/gitlab-workhorse.socket -authBackend -authSocket /run/gitlab/gitlab.socket -documentRoot /usr/share/webapps/gitlab/public

Settings nginx.conf:
upstream gitlab-workhorse {
server unix:/run/gitlab/gitlab-workhorse.socket fail_timeout=0;
server {
listen 81; # IPv4 HTTP
location ~ ^/(assets)/ {
root /usr/share/webapps/gitlab/public;
gzip_static on; # to serve pre-gzipped version
expires max;
add_header Cache-Control public;
location / {
client_max_body_size 0;
proxy_read_timeout 60;
proxy_connect_timeout 60;
proxy_redirect off;
proxy_set_header Host $http_host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-Ssl on;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;

Thanks for any help in this matter!

Best regards,