It won't let me file saying the IRS hasn't finalized one or more of my forms. What form is this and what is taking so long?

Sometimes the IRS has a delay in releasing certain forms. You can click on Review on the left-hand side of your TurboTax Online screen and your forms and dates available will be displayed. Along with a link that will allow you to get email notifications and updates on your form(s) availability.

Here is a list for your reference:

https://ttlc.intuit.com/replies/3319876