Not able to restore deleted message thread.

I have an iPhone on 16.3.1 and a mac on 10.13.6. iCloud is enabled for iMessage.

(Why am I still using High Sierra? My m1 air was stolen and I have to make do with my old macbook until I can replace it.)

I was using messages on mac and accidentally deleted a conversation trying to delete a line of text with [command] + [backspace]. There is no option to restore on the mac.

With iOS 16 and greater, you are supposed to be able to restore iCloud messages that have been deleted. The iPhone has been on iOS 16 since the update was released. I should be able to restore the thread right? No!

Although the 'Recently Deleted' Filter does show up, It is blank and there are no threads listed. I have found some chat files in the ~/Library/Messages folder but no way to restore or import them back into iMessage. What can I do? These messages have sentimental value and I would go to great lengths to restore them.