Since Drupal 8 end of life in November 2, 2021 I've had to perform (and still am) a lot of Drupal 8 to Drupal 9 upgrades in my day job(s). Drupal 8 to Drupal 9 is a significantly easier upgrade than going from Drupal 7 to Drupal 8 but it can still take a bit of work so here's what I learnt from upgrading 4 different Drupal 8 sites recently!
