PHP 7.3 will reach its end of support in December 2021. The Adobe Commerce 2.3.7 release includes support for PHP 7.4. It is suggested that merchants upgrade to the 2.4 version. Since support for PHP 7.4 in 2.3.7 is intended only to help merchants maintain PCI compliance until they can upgrade to 2.4.
Adobe Commerce 2.3 reaches end of support in April 2022. Adobe Commerce 2.4 will remain compatible with PHP 7.3, however it is recommended that merchants who have upgraded to 2.4 also upgrade their PHP to 7.4. All merchants to upgrade to PHP 7.4 before December 2021, even the ones still using Magento 2.3.