~/Library/Messages/Attachments
You can also open your Mac's Settings app , go to General > Storage and click the Info (i) icon . From there, you can see a user-friendly breakdown of all attachments saved by the Messages app.
Select the file you want (hold Command to delete multiple files) and click Delete in the lower right corner to delete the file. You can also preview the file accurately by pressing the spacebar on the keyboard.
If you're tired of manually deleting old messages and chats on your Mac, you can set the Messages app to automatically delete messages after a specific period of time. Follow these steps:
Now, your Mac will only store messages for the amount of time you set, and you won't need to manually delete them.
You can quickly delete individual messages or entire iMessage threads on your Mac using any of the methods discussed. But remember that deleted messages will also disappear from other devices if you have iCloud enabled for the Messages app. So be careful when cleaning up your Messages app and make sure you have a backup in case you accidentally delete something valuable.