[Qdulf]

The push for messenger interoperability is a reaction to the EUs Digital Markets Act (DMA), which requires certain gatekeeper services to allow interoperability with smaller platforms.

Threads is working on implementing ActivityPub for interoperability with other platforms that already use it. ActivityPub is an open standard for implementing the Fediverse, a group of federated social platforms heavily based in the open source community.

[LorenDB]

Nope, Matrix has been pushing interop for years (since the late teens).

[Aachen]

Not like it's new, though? The Internet is literally interoperating networks, emails hop from server to server until they reach the user-specified destination server, DNS delegates zones to other servers. These are protocols older than I am, and I've had a driver's license for longer than Matrix exists. Their push is amazing but not by any means unique