Showing things that got cancelled is always tough. In my time I found a couple loopholes that have helped out which might apply to your situation:
-Were cancelled projects ever socialized externally? IE something that might have been shared at a trade show, customer meetings or some other event not covered under an NDA? I had a “secret” project which later became used as a public tech demo, and once it ended up on Youtube it was no longer a concern to show it even though it was never a released product.
-Do your cancelled projects show some particularly valuable piece of your process that can’t be illustrated via another project? You may be able to get away with sharing some concept sketches for an unreleased product, depending on the field you are in and the amount of IP behind it. If you design smart phones and you share 50 concepts for a 5" smartphone, in reality you probably are not giving away any IP - people know what phones look like. If you were working on a top secret next-gen industry leading thing, that’s another story. I would not walk into an interview and say “Hey here’s the Apple self driving car I was working on”.
-Can you “Anonymize” your concept? This is common in UX where changing the clients name and any important content lets you show that you worked on a popular “E-commerce site”, but not “I worked on the cancelled version of Macys.com”. In the hardware world this could be something as simple as removing any ultra-unique features from renderings/views, getting rid of logos, and just using pieces of the project to explain “here’s the best rendering I ever did” or “look at these 300 foam models I made for a handheld widget that got cancelled”.
I know people who have gotten fired for sharing client concept work - it’s a very small industry and you never know if your new interviewing manager is your current managers former college roommate. If any part of you feels that you shouldn’t show it, then you probably shouldn’t.
As mentioned, if your portfolio is too weak without these projects, consider looking at your weakest skills and doing a project that specifically demonstrates your skills in that area. Does your portfolio not show your awesome CAD skills because your company makes garage door openers? Spend a few weekends modeling a sports car.
You can always go with the “Show it anyways” and pray approach, but you have to decide if the risk is worth the squeeze. This is especially dangerous if you are interviewing at any company that could be considered a direct or indirect competitor. Showing concept work from Nike to Addias is bad form. Showing work from Qualcomm to Nike…probably not so much.