How can I transfer messages from my MAC computer to my iphone X?

>System Preferences>iCloud Drive>Messages

can simply enable that feature on your Mac, and it will upload all your old messages to iCloud. Enable it on your iPhone, and it will download them all.

What does iCloud back up? - Apple Support

https://www.macworld.co.uk/how-to/iphone/back-up-transfer-texts-iphone-3525410/

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alternatively:

use the Handoff feature to transfer the conversation in Messages on your Mac to your iPhone.

Connect your iPhone, iPad, iPod touch, and Mac using Continuity - Apple Support
http://support.apple.com/en-us/HT6337

You can only view the messages if you sign with the same Apple ID in iCloud account on Both Macs or even you use a Mac and iOS device , but there is no feature of transferring messages , I tried in my Mac and ios device , also consulted with the apple support , not possible as both machines have different system files .

Are you trying to achieve something like this https://ios.gadgethacks.com/how-to/sync-all-your-messages-with-icloud-ios-11-4-0 182339/

If so, wait for Apple to release the next macOS and iOS updates and with luck we may get the option of “Messages” under iCloud.

Then, if I understand correctly, you first enable “Messages on iCloud” on the device containing the best/complete set of data, and when that has uploaded to the cloud you then enable same on all the other devices you wish to have this similar data. Once done any changes on one device will filter through to all the others.

You can see these articles macOS Sierra: Copy and paste across devices

macOS Sierra: Pick up where you left off with Handoff

macOS Sierra: Use AirDrop to send files to devices near you

If you follow these steps in the articles nothing is written about copying and pasting messages so its not possible .