To get ready for Drupal 10, we want to help upgrade as many Drupal 8 contributed projects (modules and themes) to Drupal 9.
As of April 11, 2021, there are 5,407 Drupal 8 contributed projects compatible with Drupal 9 and 4,712 Drupal 8 contributed projects not yet compatible with Drupal 9. Of those, 1,922 only need a one line change in their info.yml file.
To help contribute on this topic, please see this meta issue with instructions: