nginx server shows 403 error: directory index of > "/home/deploy/my_app/current/public/" is forbidden

Environment:

Digital Ocean Ubuntu 18.04 droplet, nginx installed, application in Ruby
on Rails, Using capistrano for deployment. (It uses a user called deploy)

Everything was working fine earlier.
I got message on Digital Ocean, and then I upgraded a few packages on Digital Ocean Ubuntu 18.04 LTS server. Since then, the site has been broken and I get 403 errors.

Using $nginx -V, I verified that the version got upgraded from 1.12.2
to 1.18.0

403 forbidden error

$sudo tail /var/log/nginx/error.log Following error is shown.

2021/01/11 21:58:55 [error] 5678#5678: *1 directory index of
"/home/deploy/my_app/current/public/" is forbidden, client:
999.888.255.141, server: *.myserver.com, request: "GET / HTTP/2.0", host: "hmm.myserver.com"

/etc/nginx/sites-available/default file:

server {
        listen 80;
        listen [::]:80;
        server_name *.myserver.com;
        return 301 https://$host$request_uri;
}
server {
        listen 443 ssl http2;
        server_name *.myserver.com;
        passenger_enabled on;
        rails_env    production;
        root         /home/deploy/my_app/current/public;
        ssl_certificate /home/deploy/letsencrypt/fullchain.pem;
        ssl_certificate_key /home/deploy/letsencrypt/privkey.pem;

        # redirect server error pages to the static page /50x.html

}

$ sudo view nginx.conf file:

user www-data;
worker_processes auto;
pid /run/nginx.pid;

events {
        worker_connections 768;
        # multi_accept on;
}

http {

        ##
        # Basic Settings
        ##

        sendfile on;
        tcp_nopush on;
        tcp_nodelay on;
        keepalive_timeout 65;
        types_hash_max_size 2048;
        # server_tokens off;

        # server_names_hash_bucket_size 64;
        # server_name_in_redirect off;

        include /etc/nginx/mime.types;
        default_type application/octet-stream;
        ##
        # SSL Settings
        ##

        ssl_protocols TLSv1 TLSv1.1 TLSv1.2 TLSv1.3; # Dropping SSLv3, ref: POODLE
        ssl_prefer_server_ciphers on;

        ##
        # Logging Settings
        ##

        access_log /var/log/nginx/access.log;
        error_log /var/log/nginx/error.log;

        ##
        # Gzip Settings
        ##

        gzip on;

        # gzip_vary on;
        # gzip_proxied any;
        # gzip_comp_level 6;
        # gzip_buffers 16 8k;
        # gzip_http_version 1.1;
        # gzip_types text/plain text/css application/json application/javascript text/xml application/xml application/xml+rss text/javascript;

        ##
        # Phusion Passenger config
        ##
        # Uncomment it if you installed passenger or passenger-enterprise
        ##

        # include /etc/nginx/passenger.conf;

        ##
        # Virtual Host Configs
        ##

        include /etc/nginx/conf.d/*.conf;
        include /etc/nginx/sites-enabled/*;
}


#mail {
#       # See sample authentication script at:
#       # http://wiki.nginx.org/ImapAuthenticateWithApachePhpScript
#
#       # auth_http localhost/auth.php;
#       # pop3_capabilities "TOP" "USER";
#       # imap_capabilities "IMAP4rev1" "UIDPLUS";
#
#       server {
#               listen     localhost:110;
#               protocol   pop3;
#               proxy      on;
#       }
#
#       server {
#               listen     localhost:143;
#               protocol   imap;
#               proxy      on;
#       }
#}

$ which ruby

/home/deploy/.rbenv/shims/ruby

$ sudo passenger-memory-stats
This shows as:

Version: 6.0.7
Date   : 2021-01-11 23:58:57 +0000
------------- Apache processes -------------
*** WARNING: The Apache executable cannot be found.
Please set the APXS2 environment variable to your 'apxs2' executable's filename, or set the HTTPD environment variable to your 'httpd' or 'apache2' executable's filename.


--------- Nginx processes ----------
PID   PPID  VMSize    Private  Name
------------------------------------
6884  1     175.0 MB  0.7 MB   nginx: master process /usr/sbin/nginx -g daemon on; master_process on;
6885  6884  175.2 MB  0.8 MB   nginx: worker process
### Processes: 2
### Total private dirty RSS: 1.47 MB


--- Passenger processes ---

### Processes: 0
### Total private dirty RSS: 0.00 MB

$ ps aux | grep nginx shows as:

root      6884  0.0  0.1 179176  5712 ?        Ss   Jan11   0:00 nginx: master process /usr/sbin/nginx -g daemon on; master_process on;
www-data  6885  0.0  0.3 179436 11352 ?        S    Jan11   0:00 nginx: worker process
deploy    8438  0.0  0.0  12940  1012 pts/0    S+   00:24   0:00 grep --color=auto nginx

$ ps aux | grep passenger shows as:

deploy    8478  0.0  0.0  12940   936 pts/0    S+   00:29   0:00 grep --color=auto passenger

I have restarted nginx several times. I have also tried reinstalling the Rails application.

I found this link. See section "Permission denied".
But on my server, there is no file /Users/phusion/Sites/rack.test. In fact, the server does not even have /Users or /Users/phusion folders at all.

I am a newbie.
Any help to resolve this 403 error is greatly appreciated.