Windows 11 24H2 Update

It looks like Microsoft is updating bootmgr and / or bootmgfw.efi and / or messing around with the "EFI Partition" during this update (compared to 23H2, which did NOT update bootmgr). Sounds odd, doesn't it?

What's Odd?

A Windows 11 23H2 OS, with all the latest updates for that version, running on an MBR Drive being booted in "Legacy 'mode'" (Dell term) / BIOS mode. Hmmm. That can't be, can it? Microsoft says you can't do that. And that information gets parroted all over the internet by either morons or well intentioned people who don't really know what they're talking about and have never actually tried to do that which is stated by Microsoft as "Can't be done." / "Shouldn't be done." "Isn't supported." / etc. or something like that. Funny how the English language can be used to make people think something "can't be done", when it can be done.

Anyway...

Through trial and error figured out that the 24H2 update is indeed messing around with the EFI partition and 'doing stuff'

Here's What Needs Doing

Get your old bootmgr file, delete the Windows 11 24H2 bootmgr file, and copy your old one in. Yup, it might be too late for that. But you do have a 'bare metal backup' you can get it from, right? The update process should continue.

Keeping in mind this will only happen in the unique MBR / BIOS booting situation.

Oh, and it will also leave an entry in the \BOOT\BCD as part of the update and delete the actual working boot entry, so replace the BCD file too.

Or...

Or, just change the MBR to a GPT partition, and boot in UEFI mode. With the option of changing it back, with the above noted bootmgr requirement (didn't actually try this, but should work in theory).

Knee Bone Connected to the Shin Bone...

Power Button, Computer Firmware, Legacy Boot, MBR, bootmgr (used to be ntldr), VBR / PBR, Windows, Booted!