crwdns2890332:0Big Sur from Catalina completely failed mid-cycle bricking my Maccrwdne2890332:0In my case, disconnecting the cables to the IO board did the trick. I was able to restart the Big Sur installation from Recovery Mode (using an ethernet adapter), but Big Sur ran VERY slow on my machine, so I’ve since reverted back to Catalina then Mojave. If I power off, reconnect the IO board, and power back on, I’m frozen at the black screen again, however. So I’ve left it disconnected and ordered a used one on eBay—hopefully that gets wifi and those ports working again! This seems like a very strange solution, but I’m glad I have a (mostly) working computer again. When I called Apple previously they were not helpful at all, and wanted me to get it fixed at my own cost, even though this is clearly an issue of the Big Sur update bricking quite a number of older MacBook Pros. Disappointed in Apple, as they were unwilling to do anything about it, and this has taken a lot of hours to diagnose and fix.