Usual disclaimers apply... speaking within US jurisdictions... based upon advice I received earlier in my career when asking the same question... and so on:
I created a personal website to which I would grant limited access to select portions and only to those potential employers for which I was actively considering. Not being public, there were no issues.
Alternatively, go old school and bring the copies with you on an interview. This might be hard copy screenshots, or connect your laptop to their projector during an interview such that you always retain control over the material. Then, if you can't click-through to a certain portion due to it being an unreleased feature, patent papers not yet filed, etc., you have the control to navigate to away from there.
As another person commented here, some content on my personal website were anonymized screenshots organized as a storyboard; others were full replications of the entire system's UI and server, complete with documentation and including the original company's name & logo.
Sometimes the intent to have a portfolio begins when you start the project.
Depending upon nature of your project, you may be able to create it in a way that easily accommodates an anonymous version.
For example with one particular project, I kept all of the corporate colors and logos within CSS of course but intentionally kept it isolated to a single style.css file to make it trivial to change. It was essentially a "white label" system to accommodate re-branding, co-branding, etc. (Of course, no potential employer was interested in an end-to-end recommender system with mix & match algorithms-- think: compiling regular expressions-- so I've never shown that one-- oh, the irony!)
Even if you are concerned about nondisclosures and noncompete agreements:
You can demonstrate what work you have done despite most wording within agreements because they cannot prevent you from continuing to work within your field or prohibit you from earning a living after providing labor/services under those agreement-- with a few obvious caveats.
Those caveats include explicit statements about specific items to which you have agreed, and even in some of those cases, you may still be OK based upon local laws. But you should know when you're in that situation and would of course talk to an attorney and/or your original employer.