Directly from the FDA.GOV website:
Q: Can the expiration date of an at-home COVID-19 diagnostic test be extended? (4/28/22)
A: Yes. Once the test manufacturer has more stability testing results, such as 12 or 18 months, the test manufacturer can contact the FDA to request that the FDA authorize a longer shelf-life. When a longer shelf-life is authorized, the expiration dates will be extended and the test manufacturer may send a notice to customers to provide the new authorized expiration dates, so the customers know how long they can use the tests they already have. If you did not purchase your at-home COVID-19 diagnostic test directly from the test manufacturer, you may not receive such a notice. You can check the Expiration Date column of the List of Authorized At-Home OTC COVID-19 Diagnostic Tests to see if the expiration date for your at-home OTC COVID-19 test has been extended and how to find any new expiration date.