> So to use an extension in VSCode, it has to be published in Microsoft's store?
You can always download the extension (or build it yourself) and install it manually - using Code or Codium. You can use the Open VSX registry with Code, but you have to configure it: https://github.com/eclipse/openvsx/wiki/Using-Open-VSX-in-VS....
So it technically does not have to be in MS' Marketplace, but 99% of Code user will not find or know of your extension, if it isn't in the Marketplace.
You can always download the extension (or build it yourself) and install it manually - using Code or Codium. You can use the Open VSX registry with Code, but you have to configure it: https://github.com/eclipse/openvsx/wiki/Using-Open-VSX-in-VS.... So it technically does not have to be in MS' Marketplace, but 99% of Code user will not find or know of your extension, if it isn't in the Marketplace.