@felipeelia It looks like the drag and drop sorting of Custom Results no longer works (although it's not actually throwing an error). I notice that it's using the react-beautiful-dnd library. This has been the cause of a couple of sites not being able to update to 5.9 as it's not compatible with React 17.x which is used by WordPress 5.9. So I think updating the version of React here to 17.x might've broken it. We may need to downgrade the version used by these EP features to 16. This raises an issue with #2613 that will need to be solved before that can be done.

Everything else seemed to work ok though, and I agree with the change you made to the strict value rule, at least while we're dealing with lots of relatively old CSS. Maybe after a refactor or redesign we could revisit the rule.