"This was done for tax year 2020, but the contributions and rollovers happened in March of 2021."

Which was before the return filing date, so that counts as 2020, if that was the intent.

"Do I just go to Screen 24 and enter the traditional IRA contributions (nondeductible )?"

Yes. Later, there should be 5498, showing this did get converted. And a 1099-R for 2021, which should show it is for P = prior year 2020.

"What are the steps to a backdoor Roth?"

It's a complete rollover; you pointed out there is no basis to worry about.

"Backdoor" just means, was not deductible when contributed and "rolled over" right away = conversion, but it's a nontaxable event.