Since 2017, EWWW IO has participated in an effort by a wide number of developers to encourage folks to upgrade their sites to a newer PHP release. A couple years later, the core WordPress developers joined this effort, and you can find more information about why you should upgrade here: https://wordpress.org/support/update-php/
What versions of PHP does EWWW IO support?
As of 2022-12-08, EWWW IO is currently supported on PHP 7.2 - 8.0, though 7.2-7.4 are no longer supported by the PHP core team and should be upgraded to 8.0 ASAP. We use EWWW IO on PHP 8.0 everyday, and you can see the status of the tests on various PHP versions every time we commit changes to GitHub. It works fine on 8.1 also, but we don't specifically test 8.1 or 8.2 yet. Additionally, you may encounter deprecation notices on 8.1 and 8.2, which are not errors, and can safely be ignored.