I was able to get the MBOX files to display in Thunderbird, but noneThe mbox files have only placeholders where the attachments ought to be. The attached files, if delivered to you, are in the photos_and_attachments folder. This reflects the fact that Yahoo Groups stored the attachments separately (sharing the 100 GB storage pool with Photos), if it stored them at all - which was a group option.
I also heard a rumor that the shutdown of the archives might beSee the re-worded help page:
The removal of user access to content is still scheduled for "after December 14th". At which point manual or PG Offline downloads will no longer be possible.
The only thing that has been extended is the deadline for making a getmydata request.
More Help: https://groups.io/g/GroupManagersForum/wiki
Even More Help: Search button at the top of Messages list