How will the Acquia platform migration to MySQL 5.7 affect the different versions of Drupal and the database?
Drupal 7 and 8
However, each organisations development team should examine its application is compatible with version MySQL 5.7 to mitigate risk. If your application has custom code or items in the database that are not compatible, without adequate testing the functionality may break.
To test if an issues exists with your current codebase or database, prior to your Acquia scheduled upgrade, you could replicate your production environment locally and upgrade the MySQL to 5.7.
Drupal 9 has MySQL 5.7 as a minimum requirement and will not operate on a lower version.