Organizing multiple servers with common configs in a reverse proxy

Question

I have an nginx reverse proxy set up. I have a domain that largely got setup by certbot:

server {
    root /var/www/mydomain.com;
    index index.html;
server_name mydomain.com www.mydomain.com;

location / {
    try_files $uri $uri/ =404;
}

listen [::]:443 ssl ipv6only=on; # managed by Certbot
listen 443 ssl; # managed by Certbot
ssl_certificate /etc/letsencrypt/live/mydomain.com/fullchain.pem; # managed by Certbot
ssl_certificate_key /etc/letsencrypt/live/mydomain.com/privkey.pem; # managed by Certbot
include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot

}

I now want to add sudomain.mydomain.com, but obviously want to keep the cert configs. What's the best way for me to do this? As I understand, I can move

server {
    listen [::]:443 ssl ipv6only=on; # managed by Certbot
    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/mydomain.com/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/mydomain.com/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot
}

to a separate file (maybe mydomain.ssl.conf?) and use include, and create a new server block for the subdomain. Googling suggests that I can do it all within one server block but I can't find actual code that does that.

I tried adding

server {
    server_name personal.rohitsodhia.com;
location / {
    proxy_pass http://127.0.0.1:8000;
}

listen [::]:443 ssl ipv6only=on; # managed by Certbot
listen 443 ssl; # managed by Certbot
ssl_certificate /etc/letsencrypt/live/rohitsodhia.com/fullchain.pem; # managed by Certbot
ssl_certificate_key /etc/letsencrypt/live/rohitsodhia.com/privkey.pem; # managed by Certbot
include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot

}

But I get an error for duplicate listens options.