Can anyone please recommend a direct contact for TurboTax customer service? The chatbot refuses to connect me with a human, as it doesn't recognize my question.

Once a tax return has been Accepted by the IRS or a State, TurboTax receives no further information concerning the tax return or the status of any tax refund.

The IRS will send you a letter in a few weeks explaining what they changed in the 2020 tax return that was filed to reduce the amount of the federal tax refund.  If you disagree with the IRS changes there will be a procedure in the letter for how to dispute the IRS changes.

Call the IRS: 1-800-829-1040 hours 7 AM - 7 PM local time Monday-Friday
When calling the IRS do NOT choose the first option re: "Refund", or it will send you to an automated phone line.
So after first choosing your language, then do NOT choose Option 1 (refund info). Choose option 2 for "personal income tax" instead.
Then press 1 for "form, tax history, or payment".
Then press 3 "for all other questions."
Then press 2 "for all other questions."
- When it asks you to enter your SSN or EIN to access your account information, don't enter anything.
- After it asks twice, you will get another menu.

Press 2 for personal or individual tax questions.
Then press 4 for all other inquiries
It should then transfer you to an agent.
Or you can contact your local IRS office. See this IRS website for local IRS offices - http://www.irs.gov/uac/Contact-Your-Local-IRS-Office-1 or call 1-844-545-5640 to set up an appointment
Or you may want to contact a Taxpayer Advocate in your area. See this IRS website for Taxpayer Advocate in your area and a toll free number - http://www.irs.gov/Advocate/Local-Taxpayer-Advocate

No one at TurboTax is going to know why your refund was less.   The IRS does not share any information with TurboTax after you file your tax return.   You will have to find out from the IRS.   They send a letter to explain when they reduce your refund.