Re: How do you turn off collaboration sharing in iMessage ?
We do not know which iOS version is installed on your iPhone 12 Pro Max.
For iOS 17 (else choose the iOS version at the top of the linked article below for accurate info. for your device)
Apple support's online article: Collaborate on projects with Messages on iPhone - Apple Support
says how to:
"Stop collaborating on a project in Messages:
The apps where the collaboration happens usually control access to the project. For example, if you’re collaborating on a document in the Pages app, the Pages settings take precedence over the Messages settings.
You can, however, unsend or delete the invitation from the conversation just as you would any other message.
Important: When you delete an invitation from a thread, that conversation is no longer associated with the collaboration, but it doesn’t remove participants from the file.
NB: Check participant access in the app to remove viewing or editing privileges completely."
If needed: Messages Support website : (info. / support / contact )
Messages for iPhone, iPad, Apple Watch, and Mac - Official Apple Support