I am able to setup an Apps Scripts project to create a gmail add-on and can test it out using an @gmail.com account but the option to install developer add-ons does not show up in my G Suite account.
Alternatively, how do you deploy a gmail add-on to a private domain? i tried following this https://developers.google.com/apps-script/add-ons/domain-wide but it would not let me save the configuration if all I had selected was the 'Gmail add-on extension' checkbox.
Thank you.
Domain users are now able to publish a Gmail add-on private to their own domain. Furthermore, domain private add-ons do not require a Google review, you are free to build them and publish them at your leisure.
See the documentation here: