Can I duplicate or clone an entire project?

No. There is no way to clone or duplicate a whole project (application) together with all of its settings, platform configuration, content and integrations into a new one.

What you can do is copy individual entities and rebuild the rest:

• Customer Journeys — use the Clone option on the journey canvas or in the Campaigns list. You can pick up to 5 destination projects, including other projects in your account. Choose Keep messages content and every preset used in the journey is copied along with the structure; choose Clear messages content and the message nodes come over empty. Presets do not stay in sync across projects — after cloning into a different project, edits to the original presets are not applied to the copy.
• Push presets — hover a preset in Content → Push Presets, open the three-dot menu (⋮) and choose Clone.
• Email templates, Rich Media / In-apps, SMS and other channel presets — each has its own clone action in its list.
• Segments — can be duplicated and re-pointed, or rebuilt from an existing segment.

Everything else — platform credentials (APNs key, FCM service account JSON), events and tags, API tokens, integrations, dashboards and billing-level settings — must be configured manually in the new project.