Even I am facing the same problem,when I connect external monitoprs, it seems ot show, but in few seconds all monitors don't get signals..its is frustrating
In generall I have been having a lot of issues with Big Sur upgrade...I have MBP2019
1) Very slow booting
2) TouchID not working (insipte of resetting SMC)
3) external monitors not working
4) the system goes to zombie mode for sometime, and doesn't respond
I regret for upgrading, I lost 4 days of work because of this!!! loosing respect for apple. Moved back to Windows to continue with my work
abvijay
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