I just upgraded my site Drupal from 8.8.2 to 9.3.0 using composer. Also I am now planning to use domain access module instead of multisite feature because I want to share not only the code base but also the database. Also I am sharing my Drupal upgrade runbook in case you want to do the same.
Drupal upgrade runbook: https://ravi.pro/blog/mastering-drupal.html
#Drupal #Composer #Drupal9