Is there an OOP alternative to hook_entity_operations_alter() in Drupal 8
The operations originally come from UserListBuilder. You can extend this class and alter User entity info to point list builder property to your class. The problem is that you need to implement hook_entity_type_alter wich is not in OOP land :-).

I suggest you keep this hook until Drupal become a true OOP application.

This article contains a quck comarision of hooks vs OOP events.