Meta, which in 2020 introduced the ability to send messages to Facebook users from Instagram and vice versa, has been abandoning this feature since mid-December, reports 9to5Google.

The official support page on Instagram has details of what exactly will stop working when the new changes come into effect:

You will not be able to start new conversations or calls with Facebook accounts from Instagram.
Any existing Instagram chats you have with Facebook users will become read-only, even if the Facebook users are removed from the chat. This means that you and other people with Instagram accounts cannot send new messages in these chats.
Facebook accounts will not be able to see your activity status or whether you have viewed a message.
Any existing chats you have with Facebook users will not move to your Facebook or Messenger inbox.

So far, Meta has not commented on this decision.