We use three MBPs in our home office... the only one working right is the one we didn't allow to upgrade to Big Sur. The Early 2017 15" model was fine on Catalina. It had never once missed a beat. Coconut Battery said 94% and 325 cycles BEFORE upgrading to Big Sur. Four days after upgrading to Big Sur that machine got the red battery of death and sat at 1%. Dies as soon as you remove the power cable, and demands battery service. Curious thing is that Coconut Battery now says 83% battery but still 325 cycles. The 2018 15" model lasted slightly longer. It showed the red battery, 1% and Service Recommended two days after the 2017 unit. Coconut battery says 96% battery and only 128 cycles - so this machine is like new. Both machines are now desktops rather than laptops because they do not function without a power cable at all times. I am absolutely disgusted with this. So much so that when my office asked if I wanted a replacement machine sent out so that I at least had a laptop, I asked for a Razer Pro 17 instead. Shame on you Apple - fix your damn software