The amount shown in box 12 with code W must be reported on Form 8889 included with your tax return. This is generally done by entering the W-2. However, if doing so causes TurboTax to complain about a W-2 with $0 in box 1, the code-W amount can also be caused to appear on Form 8889 without entering the W-2 itself by going to the HSA section in TurboTax, indicating that you put money into the HSA, that your employer told you about other contributions, then entering the amount as contributions for 2021 that your employer did not include in box 12 of your W-2.
Also check the W-2 to see if any of the box-13 boxes are marked. If so, the W-2 must be entered.
