I will try and clear your understanding of using iCloud for Messages vs not using this and how it is related to computer and iCloud backups.
If you use iCloud for Messages:
- Your messages (iMessages and SMS Messages) are backed up to iCloud in a separate item category.
- Your messages are also synced across all your devices that are signed on to the same Apple ID.
- These messages are NOT backed up in backup files on iCloud or on a computer. If you delete a message on one device, then it gets deleted on all your devices.
- If you delete a message then it is instantly removed from iCloud and all your devices and cannot be retrieved.
If you do NOT use iCloud for Messages:
- Your messages will NOT be backed up as a separate category on iCloud.
- Your messages are NOT synced across all your devices that are signed on to the same Apple ID. The Handoff and Continuity will continue to work so you will see the same sent and receive messages on your devices, however, if you delete on one device, then it will not be deleted on other devices.
- Messages WILL BE backed up in backup files created on iCloud and/or on a computer.
- If a past message has been deleted, then it can be recovered by restoring your entire iPhone from an iCloud or a computer backup. That deleted message has to be a part of the backup that was created on iCloud and/or a computer prior to deletion.
Hopefully, I have not created added confusion and provided some clarity to your question.
Axel F.