The limit of only being able to save three projects at a time was removed from Pro Tools | First in April 2019. It’s now possible to save as many projects as you like locally on your computer. 

You can get the latest version of Pro Tools | First from Avid’s website. Go to 'My Account' > 'My Products' > 'My Products & Subscriptions' > 'Product Details and Download Links' - 'Show'. 

Once you have updated, you can save a project locally by un-ticking the ‘Backup to Cloud’ option for the project in the Pro Tools | First projects dashboard:

There is still a limit of 3 cloud Projects.