You do not report your 3921 on your tax return, but information from the form can aid in determining your basis for the stock options exercised.  Often people overpay on their taxes due to not correctly entering their basis.

See this for where to entered the Form 3921 - https://ttlc.intuit.com/community/taxes/discussion/where-do-i-enter-form-3921-information-turbotax-2...

So does it mean if I didn't sell the exercised stock options, then the form 3921 is not required to report? If that is the case, then why Turbotax continues to ask me to fill the form 3921 information when I go through the exercised stock option questions?

If you purchased (exercised) the stock option, at the price set by the option (grant price), you must submit form 3921 regardless whether or not you sold the stock.

@Annie2023