The main new feature in this update is that it's now possible to import/export all of the created app content (character profiles, created sources, and created spells), either via the clipboard or using JSON files (#114). Other changes include updating the text of the spells that got changes in the errata for Xanathar's (#118), and fixing an issue where the concentration string was not added to cantrips in the spell table view (#116)
Full Changelog: v4.2.0...v4.3.0