Related QUestion: Does anyone know what happens if you have moved since filing your 2019 taxes but you have not set up direct deposits through the IRS?
If you did not provide your bank account information (either because you were getting a refund and wanted a paper check instead of direct deposit, or you didn't do direct debit through your e-file tax program), then they will mail a paper check.
If they have your 2019 taxes on hand, they will mail a paper check to the address on your 2019 return. Then, within 15 days of mailing you that paper check, they will mail a separate notice to you about the check.
If I were in that situation, I would make very sure that I had my address forwarded with the US Post Office. The check (and the notice afterwards) should then be forwarded to your new address.