16", i9, 32GB RAM, 5500M Big Sur is still a mess. Lagging, application windows take 5-10 seconds to open (Apple Music, iMessage,...). System is swapping gigabytes of memory without any reason and trashing the SSD. When mouse polling rate is above 250Hz, Window Server and AppleUserHID process cause very high CPU loads. I reported all of those issues, they probably haven't even looked at it. And the upcoming Xcode (12.5) forces us to use Big Sur. Great move Apple. Planned obsolescence is working as intended, huh?

You can use a tool called gibMacOS that can download the macOS 12 installer from Apple's Server without the need to enroll your system. Just install the "InstallAssistant.pkg" after download and then the macOS 12 Installer app bundle will be in your Applications directory. It's the exact same app bundle that the Software updater would download.

I somehow feel it could have something to do with HDCP. I also have that issue with my HP G2 Dock. Not only does it crash the machine, but regularly starts to stutter on the external screen (once every few seconds). If you then look into log console you will find lots of lines about stalled HDCP actions that come exactly when the stutter occurs. The latest firmware update of the G2 dock did indeed brought some HDCP fixes (mostly for HDCP 1.4 <> 2.2 switching). For now, I just connected the Monitor to the Thunderbolt downstream port on the G2 (which bypasses the DP Hub in the Dock) and have no such issues. There must be some problem with those DisplayPort Hubs and macOS. On Bootcamp there are no problems, but Windows also doesn't HDCP encypts your content if there's not reason for it. macOS does all the time if the devices support HDCP.