2021 backdoor Roth IRA conversion for 2020 tax year

In Feb  2021, I did a non-deductible contribution from my checking account to a traditional IRA ($6k for 2020) and, on the same day, requested the broker to do a ROTH IRA backdoor conversion on that full amount ($6k). 

 

My question is will this Roth IRA contribution considered for 2020 or 2021? if it's considered for 2021, does that mean I cannot do a backdoor Roth IRA coversion for 2021 any more?