I have a server block which displays properly, unless I set it to autoindex. This results in a 404 not found error.

server block:

<code> server {
# listen 80;
# server_name $domain_name;
root /var/www/html/files;
# root /var/www/html;
# autoindex on;
access_log /var/log/nginx/access.log;
error_log /var/log/nginx/error.log;
}
</code>

I solved this by adding this to nginx.conf

<--snip>
}
location /files {
autoindex on;
autoindex_exact_size off;
}
<--snip>

And this is my server block

<--snip>
server {
access_log /var/log/nginx/access.log;
error_log /var/log/nginx/error.log;
}
<--snip>

I am not sure what effect it had, but I also changed the root and sites available path from /var/www/html to /var/www

Thanks, @archer72 friend for sharing your experience with us hope it really works for us also.