FAQ - SharePoint 2019 & "Modern Mode"
SharePoint 2019 can run in the "Classic Experience" mode or the "Modern Experience" mode - even Classic sites can switch to the modern experience view.
Highlighter can only work in "Classic" SharePoint as the API's we rely on to apply custom formatting to the list are just not available in the "Modern Experience" view.
If you view a List with a Highlighter field in when you are in the Modern Experience view you will see the following error.
Clicking the "Return to classic SharePoint" link at the bottom left of the page will correct this.
If you wish to use custom formatting in SharePoint 2019 Modern Experience mode this page should help :-
