Short version:
This release (currently in preview as of August 2021) will update the comments feature in PowerPoint to the new PowerPoint modern comments experience. Modern comments help improve your collaborative experience with features such as resolving comments, anchoring comments to objects and text, and improved @mentions. Due late October to late January 2021.

Details:
The new modern comments experience will affect files where the first comment was added after this feature becomes available to you. Existing files with comments will not be affected

Modern comments can’t be read by PowerPoint 2019 or older, including subscription and perpetual versions. End users will be notified about unsupported comments in their presentations, with a prompt to open the file in PowerPoint for the web to review the modern comments.

The new commenting experience includes several popular feature requests and improves collaboration:

  • A comment will now anchor to objects. If users move the object, the comment moves with it.
  • Comments can now be anchored to text. This feature will be rolling out to Production Windows and Mac builds between June and August of 2021. Users on web and Insiders builds may have this feature earlier.
  • Comments in the margins on web. Comments will appear to the right of user’s slides by default on web, keeping their comments closer to their content.
  • Users can now mark threads of comments as resolved. Resolved comments won’t appear in the margin but can still be seen in the Comments Pane.
  • Modern comments can only be edited by the person who created them.
  • Improved notification emails let recipients see the context of the comment and reply directly from the email.
Anchoring comments with text


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Availability:
Due late October to late January 2021.

Links:
Learn more: Modern comments in PowerPoint (Microsoft.com)
For the admins:What IT Admins need to know about modern comments in PowerPoint