Proxy wildcard domains to another port

00-wildcard.conf

server {
  listen [::]:80;
  
  server_name ~^(.+)$;
  
  location / {
    proxy_pass_request_headers on;
    proxy_pass_request_body on;
    proxy_set_header Host $http_host;
    proxy_http_version 1.1;
    proxy_redirect off;
    proxy_pass http://127.0.0.1:81$request_uri;
  }
}