macOS Monterey 12.4 Messages doesn't sync all conversations with IOS iMessage & iCloud+

Thank you for the Etrecheck Report.

There are a couple of elements of particular concern which are in the below analysis and will need the User ( you ) to action

Major Issues:

Q -   Unsigned files - There are unsigned software files installed that could be malicious and should be reviewed.

A - Self explanatory and should be verified by the User. It is suggested, to download directly from a respected ASC Contributor, the application Malwarebytes for Mac. It is free or paid for added features. 

Minor Issues:

Q -  No Time Machine backup - Time Machine backup not found.

A - Worth having configured as part of a Rescue Plan. This comprises having 3 Backups using 2 methods and 1 Off Site incase of Theft, Loss or Natural Disasters. A Time Machine Backup  is very useful and can be used to Revert to Previous Working macOS.  Right now - with CCC installed, this computer is partially covered for disasters 

Q - Stuck iCloud - This computer has pending iCloud transfers.

A - This maybe related to CleanMyMac X  and the modification it has inflicted on the Operating System 

A - Any Third Party Applications that will interfere with the normal operation of the OS,  is an invitation for disaster and comprising the Operating System

Any of the below should be removed as per Developers Instructions 

This will include CleanMyMac  and do take the time to read some of the posts directly related to this application. Then, arrive at your own conclusions.

Q - Unsigned files - There are unsigned software files installed. These files could be old, incompatible, and cause problems. They should be reviewed

A - Self explanatory and need the user to review and perhaps update / upgrade or out right find replacements where required to bring in-line with Monterey 

Q - System modifications - There are a large number of system modifications running in the background.

A - Running with many system modifications, intended or not will have negative consequences on the normal operations of this computer. Some of the modification may be directly related to This will include CleanMyMac 

Q - Corrupt hosts file - Hosts file is corrupt. Configuration Files:  /etc/hosts - Count: 2 - Corrupt!

A - This too maybe related to the system modification and / or This will include CleanMyMac 

Q -  disk0 - WD_BLACK SN750 SE NVMe 1TB 1.00 TB (Solid State - TRIM: Yes) 

A - This computer is one of the few I have seen running a Third Party SSD and been able to install Monterey 

There are reports appearing on the ASC Forums regarding failed installation of Monterey on older Qualifying Apple Computers. In most cases this is related to having a NON Apple Original Internal Drive. 

The EFI Boot ROM included in Monterey is verifying for Original Apple Drive and if not found , may Balk or fail to upgrade to Monterey. 

Reports indicate the EFI BOOT ROM is Required to Flash the Computer and is a  requirement for a Successful Monterey Installation.

Network:

Q - iCloud Status: 70 pending files

A - Covered earlier re-system modification and related to CleanMyMac and possible the Open VPN

Q - Launchd: /Library/LaunchDaemons/net.openvpn.client.plist

A - Personal choice. Commercial VPNs   should only be used if Mandated by Corporate Head Office for working remotely. Otherwise - ones Privacy and Security touted by the VPN is suspect. 

Q - Kernel Extensions:  /Applications/DiskWarrior.app

A - https://www.alsoft.com/requirements

A - Note: The “Startup Disk” of macOS Big Sur (11.0), macOS Catalina (10.15), macOS Mojave (10.14), and macOS 10.13 High Sierra with SSDs (Solid State Drives) cannot be rebuilt with DiskWarrior as they are automatically pre-loaded with Apple File System (APFS). 

Q - /Applications/TechTool Pro 15.app

A - As long as this version is verified by the User as Monterey Compatible - OK 

Q - Not Loaded] CCC Dashboard (Bombich Software, Inc. - installed 2022-05-29)

 A - Good and use it myself for years. Qualifies for part of the Rescue Plan. Current version 6.1.2 for Monterey

Q -  [Not Loaded] CleanMyMac X Menu (MacPaw Inc. - installed 2022-07-18)

A - Covered earlier and again, maybe directly to over arching issue of Modification to the System including the Missing Sync element in Apple iMessages 

Q -  8 other local snapshots

A -  The above appears to be Snap Shots created by CCC and the SafetyNet feature of the same.  They occupy space on the drive until they are either removed or CCC is run more often. https://bombich.com/kb/ccc6/frequently-asked-questions-about-carbon-copy-cloner-safetynet

Pickup up on only two points from your above posting.

1 - Running 2 M1 Computer both on Monterey 12.4, 1 iPhone on iOS 15.5 and 1 Antique Mac Mini circa 2011 with High Sierra and everything is syncing across all devices. The Only exception is the Old Reminder in High Sierra does not. That is expected.

All the Above have ALL the Options enabled in iCloud and using the the Same Apple ID on all devices.

2 - iMessages is missing the " Sync " in Preferences >> iMessages . Please refer to below image.

Suggestion since elements of the OS appear to be missing for some reason >>

Understand, we are all working Remotely from all around the world. 

Therefore, we do not have the On-Hands experience the User ( you ) has with this computer.

The next best thing for us to having a semi - actual On-Hand experience  with this computer is to follow the steps below

Download the Application Etrecheck directly from a well Respected ASC Contributor. And Safe to use.

The application is free or paid from added features. 

Run the application with Full Disc Access ( Security & Privacy - Full Disc Access ).

It will take a Snap Shot -  both the hardware and software.

 The Report will Not Reveal Any Personal Information. 

Post back the Full Report - copy and paste - using the Additional Text Icon ( 3rd Icon to last )

We can have a look at the report for possible issues and may have possible suggestions to resolve the issues.

Got here since after upgrading my M1 Mac Mini to 12.4, it doesn't sync iMessages properly; iPhone and a MacBook on 12.3 still behave properly. When looking at the iMessage preferences, I do see a "sync now" button, but clicking it doesn't resolve the issue. I too tried signing out from my iCloud account and from iMessages, restarting the computer, signing back in, to no avail.

A small-scale tests shows that so far, proper iMessages do seem to sync, but non-iMessage texts (green bubles) don't, and when I try to send a text to a non-iMessage number from my Mac Mini, I get a "Not delivered" message send failure. Sending a proper iMessage still works. It doesn't matter whether I select "Start new conversations from" either the email address or the phone number associated with iMessage.

Replying to myself after resolving the issue: it turned out that after upgrading my Mac Mini to MacOS 12.4, text message forwarding from my iPhone to the Mac Mini was disabled. Moreover, Text Message Forwarding was not even an option under Settings -> Messages on the iPhone. Turning the iPhone off and back on got the menu back, and then I could set text message forwarding to the Mac Mini back on. That was half the battle. On the Mac Mini, it now only showed the email address associated with my Apple ID. Logging out from Messages on the Mac Mini, and back in, resolved that issue. non-iMessage texts (green bubles) now show up in Messages again, and I can send texts from the Mac Mini to non-iphone phone numbers.

Is " Text Forwarding " Enabled on the iPhone ? Also, while there - Is the Mac Mini listed by Name and Green Slider Green