Just another user, not connected with Apple, but I've been spending the last few months looking at ergonomic keyboards since a hand tremor has made mine unusable.
My best response is to look beyond Apple hardware for what will work best for you. Apple released a very innovative ergonomic keyboard back in the 1990s, but I don't believe they've done anything since.
https://en.wikipedia.org/wiki/Apple_Adjustable_Keyboard
A lot of keyboards can be made to work with Macs by customizing the keys to act like Mac Function keys and so on. Apps like Karbiner let you make most any keyboard do whatever you want, so triggering Mac-like keys on a Windows keyboard should be quite doable: https://karabiner-elements.pqrs.org
What I've come to believe is that there's no "most ergonomic" keyboard design. Users have different or even opposing ergonomic needs, so trying out different things is the best case to find what works for you. My personal needs require a split keyboard with adjustable "tenting" to change the angle of each side of the keyboard. And I need really stiff keys. Other people need different things, so it's hard to make one thing for everyone, except to maximize customizability (which Mac hardware isn't known for).
Outside of asking Apple to attempt an ergonomic keyboard (and waiting for that to happen), there are ergonomic keyboards available designed to work with Macs, even with Apple's keyboard symbols and functions.
I used a Goldtouch Mobile keyboard for years. It has Mac keyboard symbols (and Windows ones), and a switch on the back to make it Mac-friendly. I have heard that the wireless version may not work as well with Macs, but haven't tried it. The split-tenting feature dramatically reduced my hand/wrist pain almost immediately. My tremor finally makes me abandon them only because the keys are too sensitive. I never tried their sturdier non-mobile one, which comes in Mac and Windows versions.
https://www.goldtouch.com/ergonomic-keyboards/
Kenisis makes several keyboards that are Mac compatible. Their Freestyle 2 ones have separate Mac/PC versions (and some wireless "blue" bluetooth ones). Their newer Freestyle Pro and radical Advantage models come with extra Mac keycaps you can switch in yourself. I've never tried them.
https://kinesis-ergo.com/mac-ergonomics/
Matias has its Ergo Pro which is available in a Mac version. I'm typing on one of these, but the keys are too sensitive for my tremor.
https://matias.ca/ergopro/programmable/
After that, there's a zillion other "ergonomic" keyboards. I'm personally getting a boutique Dygma Raise, with its tenting option, and replaceable key-switches so I can get keys my tremor won't accidentally hit. It also lights up in rainbow colors 🌈😎. https://dygma.com/
