7 files declare their use of ConfigInterface in Backup and Migrate 8.4

BackupMigrate.php in lib/backup_migrate_core/src/Main/BackupMigrate.php

Config.php in lib/backup_migrate_core/src/Config/Config.php

ConfigurableInterface.php in lib/backup_migrate_core/src/Config/ConfigurableInterface.php

DrupalConfigHelper.php in src/Config/DrupalConfigHelper.php

DrupalSiteArchiveSource.php in src/Source/DrupalSiteArchiveSource.php

PluginManager.php in lib/backup_migrate_core/src/Plugin/PluginManager.php

PluginManagerInterface.php in lib/backup_migrate_core/src/Plugin/PluginManagerInterface.php