When using the extension to create a pull request, it does not ask for or allow specifying the target branch for the pull request. In my uses of it, it set the main branch as the target. It could be that it's picking the default branch, but haven't tested this to be sure. The documentation also does not state what or how it picks the target branch. This canned workflow may not apply to other users of the extension, making it less useful.
As a workaround, the extension does provide a button once the PR is created to navigate directly to the created PR in the browser, where the target branch can be changed, but this doesn't invite additional user adoption of the extension...