An extension for what tax year? There is no such thing as an "extension acceptance letter or acknowledgement code" --- so what are you trying to do?
If you had an extension for 2022----
https://ttlc.intuit.com/questions/2879424-how-do-i-print-my-4868-extension-form-after-e-filing-it-through-turbotax-easy-extension
OP here. Shouldn't there be some sort of proof that the form was submitted like a confirmation code?
Printing the 4868 doesn't prove the extension was submitted, it just proves you filled out a form.