Solved
I installed the 2021 TurboTax and have reduced the screen resolution to see the box, but it still does not let me enter the activation code. Why does the resolution need to be reduced anyway? This is a major bug.
I called the support line and they told me the solution:
Start TurboTax
When the blank Activation Screen comes up, Right Click on the Desktop to Display Settings
Change Scale and Layout to 100%
Go back to Activation Screen and enter activation code in Activation box (Ctrl V from Copied code)
The activation code will not show itself in the box
Click on Activate in lower right hand corner
Go back to Display Settings and enter in the original scale
Enter your E-mail address. We'll send you an e-mail with instructions to reset your password.