I have a 15" MacBook Pro A1707 (2017), i7-2.8G have the same issue after upgrading to Big Sur and the touchbar no more light up.According to some technician said, this is due to the upgrading process make the security chip dead. After replacing that chip will work fine but that chip is in shortage. There are too many same case in China that make the IC supplier doesn't have enough stock.
From other thread, a workaround solution is to downgrade your OS to 10.13 first, and then upgrade to Big Sur from app store.
It works for my case. Just every time boot up will see a message of "about 2 minute remaining". After finish the loading will be working fine but my touchbar is still non-function. And also need to disable the sleep, otherwise will have a system panic in my case.
Haroman
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