This is a summary of Reddit discussions and maker hacks, not of the actual market for ergonomic keyboards. Because the goal of those discussions and hacks is to be distinctive, the summary picture is fascinating but over-complicated.

Kinesis Advantage keyboards have been popular for decades and proven ergonomic benefit - mainly because the cup avoids wrist movement and the high-traffic keys are moved to the stronger thumb. Some users prefer the newer split Professional to avoid constraining arm position. These keyboards stopped my RSI cycle decades ago, and improved my speed by roughly half. (Also a US company, with fantastic support.)