You can be lean and do hardware. The whole concept of Lean was popularized and effectively used by Toyota to build cars given their unique constraints of money, space, and workers. The cycles go a lot quicker with software, but it can be used for all kinds of businesses.
One way to be lean with physical things is to run the right kinds of experiments. The most valuable thing I recall from my big company lean training was all about “design of experiments” and how using specifically designed sets of experiments which allow for a tiny number of actual physical things needing to be built and tested but you could quantify the impact of many different factors all at once. You don’t have to understand the things you test from first principles, you can have the experiments derive the equations which actually affect your product for you. The name that sticks in my head about this is Taguchi (Taguchi methods - Wikipedia).