A new version of Disable Messages has been released on the same day Drupal 9 has been released. This version fully supports Drupal 9.

With this release, the module chose to go with the fully semantic versioning model, which means, version 2.0.0 supports Drupal Core 8.8.3 or a higher version. The 8.x-1.0 release will be there for some more time to support older versions.

The 2.0.0 release mainly removes the deprecated code and uses the new solution that is supported by Drupal 9.