As you may know, your end-users can access and manage their own quarantine on Exchange Online by accessing the URL

Ok, so you need to update them and let them know to start using the new URL, now hosted within the Security and Compliance center,

Don’t worry, they will have access only to their quarantine mailbox, nothing more (unless off course you have granted them additional permissions on the Security and Compliance center)

With this move they will also have a better experience as they will be able to filter spam vs bulk, preview the message, download it as EML (to be honest I would prefer to be able to disable it from an end-user)…