You can do it 2 ways. The instructions for Schedule D are not clear for the 2020 tax, so you can choose. Since the total gain for the RSU is already updated in your wages on your W2 (you should check this by looking at your wage statement for the pay period prior to the RSU's vesting and the pay period of the RSU's vesting and maintain both wage statements for your records) the tax is already owed if you do nothing for your schedule D. That is one option.
The second option is to enter the RSU on schedule D and adjust the cost basis to the same amount as the RSU value. That will generate no additional tax obligation. The tax obligation was already created when your company rolled the value of the RSU up into your wages bucket on your W2. Like option 1, you should verify that your company did roll the entire value of the RSU into your wages bucket, as in option 1.
