What is the most ergonomic computer setup?

Ergonomics: an applied science concerned with designing and arranging things people use so that the people and things interact most efficiently and safely (Merriam Webster).

The most ergonomic setup would optimize efficiency and safety. Both of those depend on the kind of work and the person. So there’s no “most ergonomic setup,” just individual setups intended to optimize either efficiency or safety, or both. The question is analogous to asking “What is the best food?”