This version of Lightning Media requires Drupal 8.8 or later, and supports Drupal 9.
It is possible to update to this version from Lightning Media 3.x, with caveats...
When installed on new sites, this version of Lightning Media uses core tools in most cases -- it uses the Media Library module instead of Entity Browser for media reference fields and WYSIWYG embeds, and the core oEmbed system instead of Video Embed Field for remote videos (e.g. YouTube, Vimeo, etc.)