TurboTax just withdrew money from my bank account today. How do I find out what this was for

Did you choose to pay your TurboTax fees out of your Federal refund?  And if so, has your refund been delayed at the IRS?     After a period of time when there is a long delay (I think about 36 days after your original estimated refund date), TurboTax will go ahead and debit a bank account for its fees.   But you should have been getting emails warning of such and asking you to pay.  See this FAQ:

FAQ:  Why was my bank account auto-debited for the TurboTax fees?

https://ttlc.intuit.com/community/charges-and-fees/help/why-was-my-bank-account-auto-debited-for-tur...

As another possibility, this can also occur if the IRS reduced your Federal refund to a point that the fees were not covered.