How to open Gmail app (Not creating email just only open inbox) in url_launcher?

You can simple use

launch("https://mail.google.com/mail/u/0/#inbox")

This will open the inbox

You can use external dependency to open any app or playstore directly.

https://pub.dev/packages/external_app_launcher

Yes, it is possible with the url_launcher package.

To open the gmail app (inbox) with pre-filled mailto, subject and body, you can do something like this:

final Uri params = Uri(
  scheme: 'mailto',
  path: 'mailto@gmail.com',
  query: 'subject=This is the subject&body=this is body',
);
final url = params.toString();
launch(url);