how do I locate my 1040 for the year 2021?

  You have to access your own account and/or  print it for yourself using exactly the same account and user ID that you used when you prepared the return.

 https://myturbotax.intuit.com/

Start a 2024 return online and enter some personal information  so that the menu on the left opens up and lets you access your past year returns.

https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-access-my-prior-year-return/01/27010

https://ttlc.intuit.com/turbotax-support/en-us/help-article/import-export-data-files/save-2021-turbotax-online-return-pdf/L8dHfRkpT_US_en_US?uid=m5y4ch1y

Many people have multiple TT accounts and forget how to access them.  Log out of the account you are in now.

https://ttlc.intuit.com/turbotax-support/en-us/help-article/account-management/many-intuit-accounts-turbotax/L9aVfKS1Z_US_en_US?uid=ll5g6zcx

Account Recovery

Or did you use the desktop version of TurboTax?  If so, the files are on your own hard drive or any backup device you used like a flash drive.

https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/find-last-year-tax-data-file-tax-file-computer/L0XJvPaJr_US_en_US?uid=m6gufxei

https://ttlc.intuit.com/turbotax-support/en-us/help-article/data-systems/find-tax-data-file-mac/L4VNGm33S_US_en_US?uid=m6guhab0

You can get a free transcript from the IRS or for a fee of $30, an actual copy of your tax return.

https://www.irs.gov/individuals/get-transcript

https://www.irs.gov/pub/irs-pdf/f4506.pdf