Texts in published content are highlighted to identify the content as "new" or change from previous version of the same document. Users need the ability to search for this content and display the topics where the content was highlighted. Is this possible in RoboHelp 2019? Thank you in advance
There's no automatic way to do this that I know of. I always create a What's New topic that lists all the changed topics.
You could look at Dynamic Content Filters. That uses conditional tags to enable a filtering system which you might be able to use.
I also remember @Captiv8r had a nifty method years ago using See Also, that was semi-automated. His website isn't available any more though so I can't link to the details. From memory it involved setting up a What's New topic that included See Also buttons/links, then you add a see also keyword to each topic as you add or update it. The What's New topic automatically updates each time you generate with the topics that have the specificed keyword. Then for the next release you remove the see also keyword from the old topics so they are no longer included in What's New.
You don't usually see "Change Bars/Track Changes" on online content - it's much more prevalent in printed material and PDFs. Tools like FrameMaker support it better.