Under the heading "Enter Prior Year Roth IRA Contributions" should I enter zero? The IRA was closed in 2021 with zero funds remaining.

No, Prior year ROTH Contributions are all of the contributions you made prior to 2021.  

That's what I originally thought but the instructions state:

"Include only those contributions remaining in Roth IRA after subtracting any amounts withdrawn"

So since I withdrew everything there is nothing/zero remaining. So that says to me that I should report zero. 

I'm confused.

Again the key phrase is Prior Year Roth IRA Contributions.  This is everything that happened prior to 2021.  You should subtract any Prior distributions from all of the Prior contributions.

I am also confused by your answer.  He said he withdrew all prior year contributions, so would he not report zero?  Could you explain. 

Thanks

I think the same way. The instructions clearly state include those contributions remaining in Roth IRA after subtracting any amounts withdrawn. Since all the money was withdrawn according to him, there is "nothing" remaining.