Recover deleted messages

Only by restoring a phone backup, but everything else since the backup will then be lost

Yes. Anything sync’d to iCloud is not backed up to iCloud backups, if you delete them they are gone, but could have been backed up to a computer.

“Only by restoring backups” doesn’t mean they are there, but that’s the only place they could be.

According to what I've read, if you have messages going to iCloud, they are not included in backups. I ran into this same problem and they were NOT in my backup file!