How to allow users to list authorized buckets in GCP Storage?
It's not currently possible to list all the accessible buckets across all cloud projects, neither in the developer console browser nor via the gsutil command. Both of them only display buckets for one project at a time.

But if you specify a particular project (or stick with the one selected by default) you can list the accessible buckets inside that project in both gsutil (as shown in @chupasaurus's answer) and in the developer console browser. In the browser you get to the project selection popup by clicking on the project's dropdown menu in the top navigation bar.

You could try to file a feature request for it at https://issuetracker.google.com/components/187243/manage#basic, it might get accepted if it shows enough interest.