What is the best training method for non digital users?

There is no one best method. Just like some people are left or right brain dominant, people also have different learning styles.

Some people are more visual, auditory (hearing), or kinesthetic (hands-on) learners. When developing professional course material, it is standard practice to try and teach to all the learning styles.

Course material is also often tailored to the expected level of knowledge. Is the expected objective that the student remember certain terms, apply the knowledge, advance the art? That hierarchy is known as Bloom's Taxonomy, and helps identify whether a lecture and/or reading assignment is sufficient, or are practice problems or some type of advanced activity required to reach that necessary knowledge level.

That is where knowledge management becomes more about how to design training, than simply how to teach some training module.

The problem with "digital revolution" is most of the companies forgot the basement: know the final users with basement on product quality. So, there are a lot of people in this world that do not use digital devices for doing something. For example, in lot of companies, employees do not use their personal phones for doing things related to their work. That does not mean they are not "digitized people". It is about the use of digital devices for doing some things. Or lot of people still prefers a paper copy of a book instead to read it in a digital device. So, aligned with some points @Ketih stated above, the method depends on the person. In my personal experience, teaching courses and workshops around the world from years ago, the best tool I see is all related to use the pencil and the paper for doing something. When virtuality comes (no matter I am working with virtual teams from more than 25 years ago) using something very simple that replace that is the best method in my personal experience, no more than that.

From 1992 I was in charge of implementing the first IT systems in all 50+ courts of a German state.

As most users had not seen a keyboard, other than on typewriters, we started a 2 hours training to get them comfortable with computer keyboards.

Sometimes you find out you need to extend your scope in order to make your project successful.

People that are radically non-digital may be attracted to training through paper material, or also with learning through real interactive situations.