Hi @Michael Adams ,
Thanks for posting our Q&A forum.
Firstly, it is important to note that the Retention Labels and Archive Policies in Outlook on the web can be assigned to both messages and folders in your mailbox. The Retention Labels control how long your messages will be saved, while the Archive Policies control how long messages are left in an email folder before they’re moved to an archive.
Regarding your first issue, this is because the Junk Mail folder is a subfolder of the Inbox folder, which is a subfolder of the Folders folder. Therefore, the Junk Mail folder inherits its retention policy from its parent folder, which is the Inbox folder.
Regarding your second issue, this could be because your IT administrator has not turned on this option for your organization. You can check with them to see if this feature is available for you.
Reference: Retention tags and retention policies in Exchange Online
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