Just penned 7 Tips on Upgrading from Drupal 8 to Drupal 9 based on my recent experience with a multisite setup comprising 24 databases. If you are on a similar journey, I hope you find this helpful.  https://nevkatz.medium.com/7-tips-on-upgrading-from-drupal-8-to-drupal-9-648f519d6e7e?sk=fe2d0816cb852a7b5ca3dfaf0b6fa131 #Drupal