As others have noted, having an advanced degree should be a signal that the candidate is capable of deeply investing themselves into a subject area. The typecasting is ridiculous: just because you have no graduate degree but spent the first 3 years of your career working on, say, an online store, does that disqualify you from working in any other area of software engineering?

Github as CV has been debated already. Your employer may place restrictions on your ability to contribute to or publish open source. You may already be working 40+ hours a week and have other interests besides writing more code. If I'm not especially familiar with a project, I have no way to evaluate whether your contributions are valuable; I'm using the project owner's judgement as a proxy for my own. Maybe the project manager is a chump and the project is a mess, so does someone contributing 100 commits to that project count as a positive or a negative?