Browser downloads the file instead of opening php files

So, I'm posting an answer, because after the twice clean-reinstall, I have set things a but differently (to my point of view). Like I said above, I face a dilemma, since none of the config I have is the same as to any other answers I could find. For instance :

My /etc/nginx folder is basically constituted as followed :

|- /etc/nginx/
|  |- conf.d/
|  |  |- default.conf
|  |
|  |- fastcgi_params
|  |- mime.types
|  |- modules/ -> /usr/lib/nginx/modules
|  |- nginx.conf
|  |- scgi_params
|  |- uwsgi_params

There is no /sites-available or /sites-enabled as seen everywhere, the mentioned fastcgi-php.conf is actually a fastcgi_params in the root folder, my default hence is not in the site-available folder.

Here are the two configs files I now have (domain hidden under my_domain.com): First : the nginx.conf (almost untouched)

    user  nginx;

worker_processes  auto;

error_log  /var/log/nginx/error.log notice;

pid        /var/run/nginx.pid;


events {
    worker_connections  1024;

}

http {
    include       /etc/nginx/mime.types;
    include       /etc/nginx/sites-available/*.conf;
    default_type  application/octet-stream;


    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '

                      '$status $body_bytes_sent "$http_referer" '

                      '"$http_user_agent" "$http_x_forwarded_for"';



    access_log  /var/log/nginx/access.log  main;
    sendfile        on;
    #tcp_nopush     on;
    keepalive_timeout  65;
    #gzip  on;
    include /etc/nginx/conf.d/*.conf;

}

Secondly the /etc/nginx/conf.d/default.conf

    server {
    listen       80;
    server_name  my_domain.com www.my_domain.com;

    location / {
        root /var/www/www.my_domain.com;
        index  index.php index.html index.htm;
    }

    #error_page  404              /404.html;

    # redirect server error pages to the static page /50x.html
    #
    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
        root   /var/www/www.my_domain.com;
    }

    # proxy the PHP scripts to Apache listening on 127.0.0.1:80
    #
    #location ~ \.php$ {
    #    proxy_pass   http://127.0.0.1;
    #}

    # pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
    #
    location ~ \.php$ {
        fastcgi_split_path_info ^(.+?\.php)(/.*)$;
        #if (!-f $document_root$fastcgi_script_name) {
        #    return 404;
        #}
        root           /var/www/www.my_domain.com;
    #    fastcgi_pass   127.0.0.1:9000;
        fastcgi_index  index.php;
    #    fastcgi_param  SCRIPT_FILENAME  /scripts$fastcgi_script_name;
        include        fastcgi_params;
        fastcgi_pass unix:/var/run/php/php7.4-fpm.sock;
    }
    

}

I also added a line

text/php            php;

to the mime.types I also remember to delete the cache of my_domain in the browsers I use (Firefox, Opera and Chrome).

But still, the file is downloaded.

What did I do wrong ?

Edit : as I would like to make a blog.my_domain.com, shop.my_domain.com and forum._mydomain.com, I created the /site-available and /site-enabled folder, intend to create a blog/forum/shop.my_domain.com.conf in each folder of the same name located in the /sites-available, but I'm awaiting for a working config to make them visible in the nginx.conf (with an include line, right ?).

So I don't really get how these two folders work. The subdomains have their CNAME record set to my_domain.com. I also read about making a symlink for these sub-websites, but I don't really know from where to where ? Thanks again

The error log tells me the connection to /var/run/php/ is denied. the default user is www-data www-data, but my defaut nginx user is nginx (if I change it, it doens't even start.) Should I make a

chown nginx:nginx /var/run/php/

?

You lack a PHP interpreter, NGINX has an article on its wiki about FPM.