Sold stock 12/31/2020 and received $$$ into my account. Settlement date was in Jan 2021. Brokerage 1099 for 2020 doesn't show sale. For tax purposes is this a 2020 sale?

If this is a 2020 year sale, brokerage 1099 will not match tax forms.  Next year brokerage 1099 will show sale of stock actually sold in prior year 2020. How does this get reconciled by IRS?