I'll chime in with a 'me too' from multiple Mac systems (all with a T2). I was trying to go from MacOS 10.15.7 (19H15) to 11.0.1 RC2 on some test systems before GA on Thursday. Multiple forums have users with the exact same problem, so it's clearly something Apple needs to take care of. I'm certain they're aware. :-) I did a quick analysis of the HTTP URLs present in my install error log. Of the 76 unique URLs listed, 11 of them gave a 404 response, meaning about 1 in 7 were not found. Example (edited for clarity) of one 404: http://swcdn.apple.com/content/downloads/06/41/xxx/xxx/MRTConfigData_10_15.pkg. This could be unrelated and normal, or it could be that the a file required for the bridge update was not found, so it could not update, and the install failed. Pure speculation, but a reasonable possibility. If so, apple could drop the missing bits in place on the CDN, and the installers would magically start to work, maybe?