I received a tax year 2020 schedule K-1 in November 2021. It was too late for my 2020 taxes. Can I use the 2020 schedule K-1 in my 2021 taxes? How?

[DoninGA]

No.  A 2020 Schedule K-1 has to be entered on a 2020 tax return.

You will have to amend the 2020 tax return that was filed to add the Schedule K-1

See this TurboTax support FAQ for amending a 2020 tax return originally completed and filed using TurboTax - https://ttlc.intuit.com/community/amending/help/how-do-i-amend-my-return/00/27439