In the TurboTax (2023) Desktop app, I completed my tax return, went through all the reviews/checks and proceeded to eFile my return. A day later I got an email saying it was rejected. The reason was because I had not entered my IP PIN - which I didn't know I needed, and didn't know where to enter it.
The app should not have let me complete the eFile step without that IP PIN, as it is required.
On an unrelated topic: the "Choose The Platform" selection on the form where I created this forum post doesn't have enough options. It only has "Online", "IOS", and "Android". My desktop version of TurboTax doesn't fall into any of those categories, so I had to select "I Don't Know". Just sayin'.
A IP PIN is only required if you got one from the IRS. You only get an IP PIN if you were a victim of tax-related identity theft, or if you request an IP PIN. Most people do not have an IP PIN. TurboTax has no way of knowing whether you have one or not, so TurboTax cannot make an IP PIN required.