How do I unsubscribe from prototype or board notifications from Inbox?

This feature is not yet available. If you're no longer actively collaborating on a project, then you might consider leaving it completely. To learn more, check out this article: How do I remove a prototype from my dashboard?

Only consider leaving the project if you're no longer actively collaborating. Depending on the project owner and plan type, you may not be able to rejoin on your own.