Nginx downloads php files

Question

I read about this problem and tried many fixes, but none has worked. I use Ubuntu 22.04 and PHP 8.1.

My Nginx config file is now

##
# You should look at the following URL's in order to grasp a solid understanding
# of Nginx configuration files in order to fully unleash the power of Nginx.
# https://www.nginx.com/resources/wiki/start/
# https://www.nginx.com/resources/wiki/start/topics/tutorials/config_pitfalls/
# https://wiki.debian.org/Nginx/DirectoryStructure
#
# In most cases, administrators will remove this file from sites-enabled/ and
# leave it as reference inside of sites-available where it will continue to be
# updated by the nginx packaging team.
#
# This file will automatically load configuration files provided by other
# applications, such as Drupal or Wordpress. These applications will be made
# available underneath a path with that package name, such as /drupal8.
#
# Please see /usr/share/doc/nginx-doc/examples/ for more detailed examples.
##

# Default server configuration
#
server {
    listen 80 default_server;
    listen [::]:80 default_server;

    # SSL configuration
    #
    # listen 443 ssl default_server;
    # listen [::]:443 ssl default_server;
    #
    # Note: You should disable gzip for SSL traffic.
    # See: https://bugs.debian.org/773332
    #
    # Read up on ssl_ciphers to ensure a secure configuration.
    # See: https://bugs.debian.org/765782
    #
    # Self signed certs generated by the ssl-cert package
    # Don't use them in a production server!
    #
    # include snippets/snakeoil.conf;

    root /var/www/html/;

    # Add index.php to the list if you are using PHP
    index index.html index.htm index.nginx-debian.html;

    server_name _;

    location / {
        # First attempt to serve request as file, then
        # as directory, then fall back to displaying a 404.
        try_files $uri $uri/ =404;
    }

    # pass PHP scripts to FastCGI server
    #
    #location ~ \.php$ {
        #       fastcgi_split_path_info ^(.+\.php)(/.+)$;
    #   include snippets/fastcgi-php.conf;
    #
    #   # With php-fpm (or other unix sockets):
    #   fastcgi_pass unix:/var/run/php/php8.1-fpm.sock;
        #       include fastcgi_params;
    #   # With php-cgi (or other tcp sockets):
    #   fastcgi_pass 127.0.0.1:9000;
    #}
    
    location ~ \.php$ {
        try_files $uri =404;
        fastcgi_split_path_info ^(.+\.php)(/.+)$;
        fastcgi_pass unix:/var/run/php/php8.1-fpm.sock;
        fastcgi_index index.php;
        include fastcgi_params;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        fastcgi_param PATH_INFO $fastcgi_path_info;
        }

    # deny access to .htaccess files, if Apache's document root
    # concurs with nginx's one
    #
    location ~ /\.ht {
        deny all;
    }
}


# Virtual Host configuration for example.com
#
# You can move that to a different file under sites-available/ and symlink that
# to sites-enabled/ to enable it.
#
#server {
#   listen 80;
#   listen [::]:80;
#
#   server_name example.com;
#
#   root /var/www/example.com;
#   index index.html;
#
#   location / {
#       try_files $uri $uri/ =404;
#   }
#}

The output of ls -l /var/run/php/ is

total 4
-rw-r--r-- 1 root     root      5 kvě  5 16:21 php8.1-fpm.pid
srw-rw---- 1 www-data www-data  0 kvě  5 16:21 php8.1-fpm.sock
lrwxrwxrwx 1 root     root     30 kvě  5 11:12 php-fpm.sock -> /etc/alternatives/php-fpm.sock

Strange is that which apache2 returns
/usr/sbin/apache2 but sudo apt remove/purge apache returns that apache is not installed. I did not install apache explicitly, so I don't know where the file /usr/sbin/apache2 come from.

Do you have any ideas how to proceed. Thanks a lot.

EDIT: I added debug keyword into nginx error log settings, now the following lines emerge in the error log when I restart nginx:

2022/05/07 19:16:31 [debug] 87790#87790: epoll add event: fd:7 op:1 ev:10000001
2022/05/07 19:16:31 [debug] 87791#87791: epoll add event: fd:7 op:1 ev:10000001
2022/05/07 19:16:31 [debug] 87790#87790: epoll add event: fd:8 op:1 ev:10000001
2022/05/07 19:16:31 [debug] 87791#87791: epoll add event: fd:8 op:1 ev:10000001
2022/05/07 19:16:31 [debug] 87792#87792: epoll add event: fd:7 op:1 ev:10000001
2022/05/07 19:16:31 [debug] 87792#87792: epoll add event: fd:8 op:1 ev:10000001
2022/05/07 19:16:31 [debug] 87793#87793: epoll add event: fd:7 op:1 ev:10000001
2022/05/07 19:16:31 [debug] 87793#87793: epoll add event: fd:8 op:1 ev:10000001
2022/05/07 19:16:31 [debug] 87794#87794: epoll add event: fd:7 op:1 ev:10000001
2022/05/07 19:16:31 [debug] 87794#87794: epoll add event: fd:8 op:1 ev:10000001
2022/05/07 19:16:31 [debug] 87795#87795: epoll add event: fd:7 op:1 ev:10000001
2022/05/07 19:16:31 [debug] 87795#87795: epoll add event: fd:8 op:1 ev:10000001
2022/05/07 19:16:31 [debug] 87796#87796: epoll add event: fd:7 op:1 ev:10000001
2022/05/07 19:16:31 [debug] 87796#87796: epoll add event: fd:8 op:1 ev:10000001
2022/05/07 19:16:31 [debug] 87797#87797: epoll add event: fd:7 op:1 ev:10000001
2022/05/07 19:16:31 [debug] 87797#87797: epoll add event: fd:8 op:1 ev:10000001
2022/05/07 19:16:31 [debug] 87798#87798: epoll add event: fd:7 op:1 ev:10000001
2022/05/07 19:16:31 [debug] 87798#87798: epoll add event: fd:8 op:1 ev:10000001
2022/05/07 19:16:31 [debug] 87800#87800: epoll add event: fd:7 op:1 ev:10000001
2022/05/07 19:16:31 [debug] 87800#87800: epoll add event: fd:8 op:1 ev:10000001
2022/05/07 19:16:31 [debug] 87802#87802: epoll add event: fd:7 op:1 ev:10000001
2022/05/07 19:16:31 [debug] 87802#87802: epoll add event: fd:8 op:1 ev:10000001
2022/05/07 19:16:31 [debug] 87805#87805: epoll add event: fd:7 op:1 ev:10000001
2022/05/07 19:16:31 [debug] 87805#87805: epoll add event: fd:8 op:1 ev:10000001