Zombie messages deleted on iPhone showing on iMac

I have an iPhone 13 Pro running iOS 18.1. When I delete a text message on my phone and take the additional step to permanently delete it from my "Recently Deleted" folder, they still show up in the Messages app on my iMac running MacOS Sequoia 15.1. Why are these zombie messages that I've permanently deleted from my phone still showing up in Messages on my my iMac?

On my iPhone, I have iMessage turn ON. On my iMac, I have "Enable Messages in iCloud" enabled and have clicked "Sync Now." It has no effect.

I shouldn't have to delete individual messages from each device. When I delete them from my iPhone, I don't want to see them on my iMac. Why are aren't text messages on my two devices mirroring each other?