Emails sent from all senders with mutimedia attachments are being quarantined. But you want to allow one sender to by pass that rule.

There are no options on File Filtering rules to exclude users.

This behavior is by design.

Workaround

Disable the File Filtering rule and create a content filtering rule with user exceptions.  See the following article for steps on how to use user exclusions with content filtering rules: How to Exclude Specific Email Sender From Actions of a Content Filtering Rule.