Having this same issue since the latest public release (Beta 10 I believe.) On 2019 16" MacBook Pro, login and get about a third of the way on the status bar logging in then fan kicks in and Mac abruptly turns off. I can login via Safe Mode and also can pull up Recovery Mode. Tried a clean install of Big Sur beta and still have the same issue. Tried the Recovery Mode -> Unlock Startup disk trick a few times and still no go. Reset SMC and others to no avail (just took longer before it inevitably flared the fans and shut off.) Anyone have any other solutions that worked? Been without the use of that MacBook Pro for a week now (safe mode is super slow).