I authorized IRS to withdraw my taxes due on 8/26. They still have not withdrawn the money as of 9/9/21. How can I check the status of this tax payment withdraw?

Go to www.irs.gov and click on "View Your Account".

The IRS is in behind processing returns and balance due returns are at the back of the long line ... the debit could take as long as a couple of months.   So if your DD info is correct then all you can do is wait for them to complete the transaction. 

Did you efile? Was it Accepted?  Better double check.  You can check your efile status here,
https://turbotax.intuit.com/tax-tools/efile-status-lookup

When you efile you get back 2 emails. The first email only confirms the transmission. The second email says if the IRS (or state) Accepted or Rejected your efile. Check your spam or Junk folder.

When you log into your account you should also see the status and if it was Accepted or Rejected, Started, Printed, Ready to Mail, etc. What does it say?