Windows 11 Insider Setup fails with 0x800B0109 before UEFI disk layout error

Your logs show two separate blockers: certificate trust error 0x800B0109 and the UEFI disk-layout message. Microsoft’s SetupDiag guidance says that when multiple failures are present, the last failure is typically fatal, so the earlier Authenticode entry does not prove it caused the rollback. First, run the latest SetupDiag as administrator and review its result together with setupact.log and setuperr.log. Then enable the CAPI2 Operational log, reproduce the signature check, and inspect events 11 and 30 for the failing certificate chain. Do not import an arbitrary root certificate. Separately, run Get-Disk and confirm the operating-system disk uses GPT. If it is MBR, back up first and run mbr2gpt /validate /allowFullOS; convert only if validation succeeds, then retain UEFI firmware mode. I cannot confirm this exact failure as a documented known issue. If both checks pass, file Feedback Hub feedback with the SetupDiag, Panther, and CAPI2 logs, build, channel, and ISO details.