MacOS Mojave 10.14.6 does not support multiple keyboard collaboration OS: Mojave 10.14.6

Laptop: MacPro 2017

Problem:
Looks like I can't use two keyboards to execute the same command collaboratively. E.g: For typing command + space, it perfectly works if I execute this shortcut only on one keyboard. However, if I press command at one keyboard, and space at another, the laptop can only recognize the space.

Keyboard combinations I've tried: 


Apple a1314 + Mac built-in keyboard
Apple a1644 (with wire and when it's wireless) + Mac built-in keyboard
Apple a1314 + Apple a1644


None of them can work with each other.

Any solution to the problem? Thanks!
OK problem solved. After installing Karabiner (originally to solve the caps lock delay), I found I can work on two keyboards at the same time. The version I installed was 11.6.0.