Users will have access to the functionality dictated by their license - for guests, you can see the full list of capabilities based on license here: https://support.microsoft.com/en-us/office/let-guests-see-your-project-in-project-for-the-web-81e1c210-74b2-4711-98ab-dea58f1b566b For more info feel free to check our service description as well: https://learn.microsoft.com/en-us/office365/servicedescriptions/project-online-service-description/project-web-service-description. I hope this helps!