Hello
Exporting a Journal Archive (archive in general) does not delete the items from storage. You specifically need to select that when exporting, and it must be 'allowed' (site, retention wise)
Retention categories delete automatically provided you have the Storage Expiry running. (site setting).
Even then, your storage migth not decrease immediately, due to using sharing and collections (look for 'sparse collections' to find article describing that.)
Regards. Gertjan
