How will I get my third stimulus if they weren't done processing my return until after they had already sent out direct deposits?

According to the IRS, they are still processing stimulus payments and you may get yours after your return is processed.

The IRS will continue to process 2020 tax returns and issue additional payments in 2021 to individuals who have not already received a third payment or who are eligible to receive an additional amount if their initial payment was not based on their 2020 tax return.

If you are in this situation and eligible for the third Economic Impact Payment or an additional amount based on your 2020 federal tax return:

• Your payments will be issued after your 2020 tax return is processed. Check your payment status in Get My Payment.
• You will receive a Notice 1444-C, Your third Economic Impact Payment, after the payment is issued. Keep this notice with your 2021 tax records.

If you do not receive a payment this year, you may be eligible to claim the 2021 Recovery Rebate Credit when you file your 2021 tax return in 2022.

[Source:  Questions and Answers about the Third Economic Impact Payment  - Requesting my payment]