I wrote this guide because I could not find any information elsewhere and I found a workaround by accident.

My hardware setup is

• Moza R21 base
  
• Moza RS v2 steering wheel
  
• Moza CRP pedals

Disclaimer: This workaround works on my machine for the above hardware. I cannot guarantee that it works on your machine and for other Moza hardware.

• Power-on the wheel/base
  
• Start Grid Legends
  
• The wheel/base functions, but there is no Force Feedback
  
• Power-off the base (hold the power-button for more than 5 seconds) - the game shows a pop-up that the steering device is changed
  
• Power-on the base - the game shows a pop-up that the steering device is changed
  
• Now Force Feedback is activated :-)

If this also works for other Moza hardware, please mention it in the comments!