If your team can see a button on the Projects Tab list views labeled New Project, this button has been deprecated. The best place to create a new Project is from a Sale record.
Resolution
Remove the New Project button from the "Projects List View" Search Layout record.
Navigate to Setup
Go to the Objects menu
Select the Project object
On the Project object page, go to Search Layouts and click Edit next to the Project List View layout:
From the Search Layout, you will remover the New Project button from the Custom Bottoms section by clicking on the name of the button and using the Remove arrow to move it into the Available Buttons column.
When finished, this setting should look like this:
Save your changes.
NOTE: If you need to do this for another Object (like Sale or Appointment) you can follow this click-path:
Object > Search Layouts > find the Object List View > Edit > allows you to add or remove custom buttons.