if you have not received your stimulus payment by the time you submit your 2020 tax return, you will reconcile on that submission how much you are due. Look closely at Line 30 of Form 1040.
The IRS will stop sending out the 1st stimulus payment this week
The IRS will be sending out the 2nd stimulus payments shortly, but stop on January 15, 2021
After that, it'll all come through on the 2020 tax return, again, Line 30.