Does not use passive listeners to improve scrolling performance

Heads up! This is a developer-level document. You need to be one or hire one to implement this optimization. It may require changes to code in your theme or a plugin.

The scrolling experience can be affected by touch and wheel event listeners and therefore, making the site feel as if it was non-responsive, so the goal is to use passive event listeners instead.

This is what’s specifically instructed: 

“Consider marking your touch and wheel event listeners as `passive` to improve your page's scroll performance.“  -  Which can be done as explained here.

You’d need to set a passive flag to every event listener that’s listed in this Diagnostic:

As you might have noticed, this requires very customized development work to be accomplished which would need to be addressed by the specific plugin/theme development teams. However, we recommend not spending too much time and energy on this one because it could have no significant impact on improving the actual performance experience or grade.

Please refer to this official article for more information.