Configure Nginx as a Reverse Proxy for Apache

You need to show us your config files, so we can better assets you.

server {
    listen 80;
    server_name www;
    rewrite ^ https://$http_host$request_uri? permanent;
    server_tokens off;
}

server {

 listen 443;
        ssl on;
        ssl_certificate /etc/letsencrypt/live/www/cert.pem;
        ssl_certificate_key /etc/letsencrypt/live/www/privkey.pem;
        server_name www;
        server_tokens off;
        # ......
        fastcgi_param   HTTPS               on;
        fastcgi_param   HTTP_SCHEME         https;



    root /var/www/nextcloud;



    index index.php index.html;
    location / {
        proxy_pass http://localhost:8080;
        include /etc/nginx/proxy_params;
    }
location ~ /\.ht {
                deny all;
}

proxy_set_header Host $http_host;
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;

client_max_body_size 1536M;
client_body_buffer_size 1600M;
proxy_intercept_errors on;
proxy_buffering on;
proxy_buffer_size 128k;
proxy_buffers 256 16k;
proxy_busy_buffers_size 256k;
proxy_temp_file_write_size 256k;
proxy_max_temp_file_size 0;
proxy_read_timeout 300;

<VirtualHost *:8080>
    ServerAdmin 
    DocumentRoot /var/www/nextcloud
    ServerName www
    ServerAlias www.
    ErrorLog logs/www-error_log
    CustomLog logs/www-access_log common
    <IfModule mod_headers.c>
      Header always set Strict-Transport-Security "max-age=7776000; includeSubDomains"
    </IfModule>


# SSLEngine off
#    SSLCertificateFile /etc/letsencrypt/live/www/cert.pem
#    SSLCertificateKeyFile /etc/letsencrypt/live/www/privkey.pem
#    Include /etc/letsencrypt/options-ssl-apache.conf
#    SSLCertificateChainFile /etc/letsencrypt/live/www/chain.pem
</VirtualHost>

Alias /nextcloud "/var/www/nextcloud/"

<Directory /var/www/nextcloud/>
  Options +FollowSymlinks
  AllowOverride All

 <IfModule mod_dav.c>
  Dav off
 </IfModule>

 SetEnv HOME /var/www/nextcloud
 SetEnv HTTP_HOME /var/www/nextcloud

</Directory>