I will be receiving my first two stimulus checks on my 2020 tax return. However I have not received my third stimulus check yet even though I am eligible. Why haven’t I?

The IRS has just started to send out Stimulus #3.   It is an ongoing process that will take a few weeks to complete. You can check your status here:

Get My Payment | Internal Revenue Service (irs.gov)

The IRS doesn't share that information with us. The IRS issues the stimulus payments, not TurboTax. This means that we can't say for sure why you haven’t received your third stimulus payment or if and when you'll receive it.

They do give us this guidance: If the IRS has received a 2020 tax return, but hasn’t yet processed it, the stimulus payments may be issued to the account on the 2019 tax return. 

• If you didn't file a 2019 income tax return or you were claimed as a dependent, your third stimulus payment will be delayed.

To be eligible for the third stimulus, you need to meet the following requirements: 

• Families earning less than $150,000 a year and individuals earning less than $75,000 a year should get the full $1,400 per person.
• Families earning up to $160,000 per year and individuals earning up to $80,000 per year will receive prorated amounts.
• One notable difference from the first two stimulus is that you will receive stimulus payments for all your dependents, including adult dependents and college students.