That button only appears sporadically, but when it has I've tried to 'press the button that appears to the left of the shift key' to identify the keyboard, but this doesn't work either. I've also tried - and failed- to use the 'set up a new keyboard' function in Bluetooth preferences.
It then asked me to enter a code, I've tried the generic 0000 as well as 1234, and even 00-00-00-00-00, but it continually fails to connect. It occasionally recognises a new device, although the MacBook picked up immediately that it was an 'ergonomic keyboard,' when the iMac recognises it it identifies it as unknown device with a serial number 00-00-00-00-00. However, when I try to pair it with my mid 2011 iMac (also running High Sierra) it just won't pair.
It paired with my mid 2011 MacBook Air running High Sierra straight away. I recently bought a Microsoft Surface Ergonomic keyboard.
