Part III would generally be needed to report any nonqualified Roth IRA distribution, but if the entire distribution was taxable, the IRS probably wouldn't question it because the default is that the entire distribution is taxable.
I had held my Roth IRA for more than 5 years when I took a distribution, and I was older than 59-1/2 so the entire distribution from my Roth IRA was NOT taxable. I would assume that the default for Roth distributions is that they are NON taxable. I just didn't report it anywhere at all in my 2018 federal tax filing.
