Keeping Messages attachments in iCloud (and maybe on iPhone) but removing from Mac

As you mentioned .

Am I good to delete these? I assume they are just local copies of files that are in the cloud and if I remove a copy on my computer, that file will remain in iCloud and/or on my iPhone. That would be a great outcome for me but I can't really find a clear answer.

When you delete attachments from Mac Delete messages and conversations in Messages on Mac - Apple Support

Set how long to keep messages

1. In the Messages app  on your Mac, choose Messages > Settings, then click General.
2. Click the “Keep messages” pop-up menu, then choose an option.
3. Important: If you choose an option other than Forever, your conversations (including all attachments) are automatically removed after the specified time period elapses.

That file will remain in iCloud and/or on my iPhone when iPhone and Mac are signed in with same Apple ID and password on the same network , the conversations are shared between them as messages box is turned on , so deleting conversations with its attachment will be deleted from Mac , iCloud and synced device iPhone .

See the article Access your messages on all your Apple devices - Apple Support

You can turn off Messages in iCloud on all your devices or on your Mac only.

1. In the Messages app  on your Mac, choose Messages > Settings, then click iMessage.
2. Click Settings, then deselect Enable Messages in iCloud.
3. Choose one of the following:

• • Disable All: Turns off Messages in iCloud on all your devices. Messages are no longer stored in iCloud and are instead stored on each device.
  • Disable This Device: Turns off Messages in iCloud on your Mac only. Messages on your Mac are no longer stored in iCloud; on any other device where Messages in iCloud is turned on, messages continue to be stored in iCloud.

I have the same problem. But it happened in a single day. I watch my hard drive memory and it’s always ~66gb. One day I try to restore an iPad, it glitches and fails. Then notice I have 44 extra gigs making my memory over 100 on my Mac hard drive. I contact Apple senior support. They have me erase everything. I end up permanently losing many files and videos. Then I contact them again and the person helping decided she won’t help anymore, or she quit. Now I’m waiting to take it to Apple Store….