This continues to be on our backlog due to prioritization of other work items. We will update when there is more to share.
Pinning the entire document library is supported today. Learn more here, https://support.microsoft.com/en-us/office/add-a-sharepoint-page-or-list-to-a-channel-in-teams-131edef1-455f-4c67-a8ce-efa2ebf25f0b.
We currently do not support pinning a specific folder, but we are considering this feature.
We are continuing to work on this feature. As with Windows notifications, we are also doing work to give users the choice between Teams notifications & Mac notifications.
We will update you as work progresses.