wireless networking – What is the speed and detail operation when several devices do a Speedtest in an MU-MIMO router simultaneously?

I have read a lot of articles that try to explain how MU-MIMO works, but I still can’t figure out how the below picture works. It shows that MU-MIMO Wi-Fi allows every device to have an ISP speed while they connected to wifi simultaneously, so how is it possible to give the maximum bandwidth to the three devices? Is it the actual happen when I do it by Speedtest?

I know MU-MIMO technology is to reduce the delay of communicating to several devices simultaneously, but when the router receives the packages, it still needs to send the packages one by one, so what is the significance of this operation? Can someone clearly explain the actual flow and the bandwidth calculation steps when three devices do a Speedtest in an MU-MIMO router theoretically? Thank you.