Nginx Reverse proxy excluding files

I've a landing page done using wordpress and is hosted on example.com. I've an app running on app.example.com on external url. When user try to access wordpress files, it should be served from example.com and if that url or folder is not available the url must be masked and must go to remote url as example.com/$1. I've tried using nginx reverse-proxy but it is not working.

location / {
    try_files $uri $uri/ /index.php?$query_string @proxy;
}

location @proxy {
    proxy_pass https://example.com/$1;
    proxy_set_header HOST $host;
    proxy_set_header X-Forwarded-Proto $scheme;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
}

The try_files only checks if actual files exist on filesystem. Once it founds a file that exists, it uses that one to serve a response. try_files does not act on any HTTP status codes.

Since you always have /index.php in your filesystem, the @proxy target is never used.

You need to implement the functionality by hooking into WordPress 404 error generation hook and perform the proxying there.