I am new to an organization that is making the move from SP 2010 to SP 2013 to SP 2016 to SP 2019. These are all on-premise versions. The site collection has almost 3500 sites. There are lots of customizations - webparts that include more content editors that point to both jquery and html files.
For testing purposes, a team upgraded from SP 2010 to SP 2013. Nothing broke - yet. My concern is when they migrate to SP 2016, and the modern pages are turned on - content editor webpart does not exist in modern pages - SPFx rules. What happens on those pages where content editor webparts have been used for purposes of pointing to files? Is there a document for the best practices?