They have warned about this before, but it’s still pretty wild to think they’re now removing old DMs (and chats, but it’s not like anyone used those).
Interestingly you can still see them if you take out your data via a request, so they got them in the database still.
GDPR is not at play here, private messages are essential data if one of the purposes of your app is messaging. But now they’ll have to delete them because they’re no longer necessary since the user can’t see them. Though it doesn’t have to be immediate.