Open protocols are better than open source

At a technical level, a piece of code available under an open source license, written in a particular programming language, can at best be "bug compatible" or APIs that interoperate with another piece of code.

A protocol with an open specification allows anyone to implement the protocol – which by definition if coded correctly, will be interoperable. You can pick any programming language, and any source code license, you like, and still have software that works together. This leads to a plurality of options, with different business, governance, and community models.

Open Source at it's core is about licensing Open Source Licensing, although I like to expand it with Three Definitions of Open Source that cover some of the accepted principles around the movement.

Protocols and the thinking around them, especially Open Social Protocols, are well explained in the 2019 essay Protocols, Not Platforms.