Where can I get copy of my lost 2020 W2 form?

You can contact your employer, human resources, or your employer's payroll service provider--whoever provides you the W-2--and ask them for a replacement copy.

Sometimes larger employers/payroll services have a website where employees can download a copy of their W-2.  You can ask your employer.

NOTE:

Also, see the Addendum I left you in my next comment below.

ADDENDUM:

If your employer or payroll services is an import partner with TurboTax, you "might" be able to import it into TurboTax, but it often requires some identifying info present on the actual W-2, so you might not be able to.  But you can read about it here:

FAQ:  Will I be able to import my W-2 before I get it in the mail?

https://ttlc.intuit.com/community/forms/help/will-i-be-able-to-import-my-w-2-before-i-get-it-in-the-mail/00/26418