Drupal is always evolving faster. Drupal 8 will be end-of-life in November 2021, which is pretty close. Drupal 7 will continue to receive support until November 2021.
If you are using Drupal 8, you must upgrade to Drupal 9 before November to keep your site secure.
With the upgrade from Drupal 8 to Drupal 9 – there is no need for migration; the new features for Drupal 9 were gradually released inside Drupal 8. The main change that Drupal 9 brings is the removal of deprecated code, much like getting a hair-cut.
