CUSTOM APPS: Client Portal?

Is there a way to build a client portal in Fibery?

I want to keep everything internally in Fibery:

Client → Projects → Tasks
Client → Documents
Client → Invoices
Client → Meetings

But then give each client their own portal where they can only see their stuff (and maybe update tasks, upload documents, comment, etc.).

Has anyone built something like this with Custom Apps?

Or would I need to build an external frontend using the Fibery API? Because I have some client that don’t want to sign up on any other tool, Just sending a link of their portal and nothing else. No login to fibery or other tools

What are the best options/workarounds for this?