I have a 16" 2019 MBP running Big Sur 11.4 and I'm use an HP Thunderbolt Dock G2 with my monitors connected via USB-C. I get this all the time. Sometimes it can be all of a sudden in the middle of a session, but it is much more prevalent when I am plugging in/out of the dock. It also occurs when the laptop wakes up after being in sleep mode. I get the quick sound of the fans blowing and then it reboots. It happens way too many times. I have no other option in terms of trying other docks. I report the error every time I get it. It has been going on since the Big Sur upgrade.