10 files declare their use of BackupMigrateInterface in Backup and Migrate 5.0.x

backup_migrate.module in ./backup_migrate.module

Primary hook implementations for Backup Migrate.

DefaultDBSourcePlugin.php in src/Plugin/BackupMigrateSource/DefaultDBSourcePlugin.php

DestinationPluginBase.php in src/Drupal/EntityPlugins/DestinationPluginBase.php

DrupalConfigHelper.php in src/Drupal/Config/DrupalConfigHelper.php

DrupalFilesSourcePlugin.php in src/Plugin/BackupMigrateSource/DrupalFilesSourcePlugin.php

EntireSiteSourcePlugin.php in src/Plugin/BackupMigrateSource/EntireSiteSourcePlugin.php

Schedule.php in src/Entity/Schedule.php

SourcePluginBase.php in src/Drupal/EntityPlugins/SourcePluginBase.php

WrapperPluginBase.php in src/Drupal/EntityPlugins/WrapperPluginBase.php

WrapperPluginInterface.php in src/Drupal/EntityPlugins/WrapperPluginInterface.php