Karabiner looks like part of what's involved. See if the following discussion helps:
Microsoft Natural Ergonomic Keyboard 4000… - Apple Community
According to the following, it might be possible to remove the drivers and access (most of?) the functions:
https://david.rothlis.net/keyboards/microsoft_natural_osx/
According to the following, Microsoft only supports add-on drivers through 10.7, and states that 10.7 through 10.10 have "Limited Functionality":
https://www.microsoft.com/accessories/en-us/products/keyboards/natural-ergonomic-keyboard-4000/b2m-00012#techspecs-connect
Interested in an alternative?
It looks like some folks have gotten (most of?) the Microsoft Sculpt keyboard working:
https://www.reddit.com/r/osx/comments/2vozkq/anyone_use_the_ms_sculpt_comfort_mouse_on_latest/
https://forums.macrumors.com/threads/microsoft-sculpt-ergonomic-keyboard-mac.1906151/
And among those ergonomic keyboards specifically for macOS: the Kinesis Freestyle2 Blue Wireless Ergonomic Keyboard for Mac, and the Matias Ergo Pro.