Missing messages after syncing new iPhone 17 to iCloud

Bought a new iphone 17. After syncing the new phone i realized that I was missing hundreds if not thousands of messages. I checked my old phone and saw that all the messages were there. Checked I cloud setings and saw that the sync messages was not selected. I activated sync messages on the old phone and it deleted the missing messages from my old phone rather than adding them to my iCloud. I had to reset the old phone from a previous backup to regain the messages. How do I get these messages added so they are visable on my new phone and computer and saved on iCloud.

[Re-Titled by Moderator]

Original Title: Syncing issues