Kodi 19.0 is represented by nearly five thousand commits since Kodi 18 and represents some big changes like finishing off the migration from Python 2 to Python 3. Kodi 19.0 also has many audio/video playback related improvements, AV1 software decoding is now supported, integer scaling is supported for those playing game emulators within Kodi, various theme/skin improvements, metadata scraper improvements, and new security improvements.
More details on the big Kodi 19.0 release over at Kodi.tv .