I have some new error messages to add to the thread: iMac17,1 (2015) running beta 4 xyz@bigsur ~ % sudo sh -c "softwareupdate -ia --verbose" Software Update Tool Finding available software 2020-08-23 20:59:54.678 softwareupdate[3811:61191] Creating client/daemon connection: BB6D4721-8450-4399-87E2-EFD67CB2E6B6 Downloading macOS Big Sur Beta 5 downloading: 100.00% Failed to download & prepare update: Error Domain=SUMacControllerError Code=7723 "[SUMacControllerErrorPreflightPersonalizeFailed=7723] Failed to perform PreflightPersonalize operation: [MobileSoftwareUpdateErrorDomain(MSU):MSUERRINTERNALERROR(7)1MobileSoftwareUpdateErrorDomain(MSU):MSUERRINTERNALERROR(7)]" UserInfo={NSUnderlyingError=0x7f8d41e05110 {Error Domain=MobileSoftwareUpdateErrorDomain Code=7 "Could not create update context in preflightpersonalize." UserInfo={NSLocalizedDescription=Could not create update context in preflightpersonalize., NSUnderlyingError=0x7f8d43806f90 {Error Domain=MobileSoftwareUpdateErrorDomain Code=7 "Update context didn't validate." UserInfo={NSLocalizedDescription=Update context didn't validate.}}}}, SUMacControllerErrorIndicationsMask=0, NSDebugDescription=[SUMacControllerErrorPreflightPersonalizeFailed=7723] Failed to perform PreflightPersonalize operation: [MobileSoftwareUpdateErrorDomain(MSU):MSUERRINTERNALERROR(7)1MobileSoftwareUpdateErrorDomain(MSU):MSUERRINTERNALERROR(7)], NSLocalizedDescription=Failed to personalize the software update. Please try again.}

Developer beta 5 will not install on my imac17,1 (2015) currently running beta 4. /var/log shows "unsupported hardware." I sent in a report via feedback assistant but have the feeling I will be waiting for beta 6 to get back on track.