How to reply from catch-all addresses on Google Workspace (G Suite)

Warning: This method requires to have the paid version of Google Workspace. And you probably shouldn't have other users in your Google Workspace while using this.

On the Google Admin Console, go to Apps -> Google Workspace -> Gmail -> Routing.

Find the SMTP relay service.

Configure an SMTP relay service to have the settings:

Save the settings and now you can set up the SMTP settings on your email client:

And done! You can now reply from any other name under your domain.