First, to correct a misconception: Reflect does not modify the boot partition. The most it does is to add some additional lines via BCDEDIT to create an entry for the Windows Boot Manager so that it can offer an option to boot into normal Windows or Reflect via a boot menu option. The code that this entry will execute is located in the Rescue Media (RM) staging area WIM (usually c:\boot\Macrium\.... ) which is where RM Builder creates it.
But none of those are involved in running Windows Defender's Offline Scan. To do that, when you invoke Windows Defender Settings -> Offline Scan, it tells Windows to reboot from the Windows Recovery partition, and passes the pathname of the Windows Defender Offline Scan program for the Recovery software to execute after it is up and running.
I'm running Windows 11 23H2 223631.2715 and MR 8.1.7762 --- and I just invoked the offline scan; it took ~8 minutes, and didn't find anything before it rebooted itself. The biggest pain was that I had to look up the Bit Locker Recovery key and enter it so the scan could work with an unencrypted disk.
I seem to remember from recent earlier posts that you have your recovery partition on a different disk than the OS, so I wonder if you made the same mistake that I did a while back. I had removed an obsolete Recovery Partition between the system partition and a new Recovery Parition. I forgot that this would renumber the partions thus causing attempts to invoke the offline scan to fail. The problem was ultimately remedied by updating the recovery information using the REAGNTC command -- in my case changing from parition 5 (now nonexistent) to paritition 4 (its new location).
Right now, my system disk has 4 partitons: EFI, MSR, System, and Recovery. The REAGENC /INFO shows:
Windows Recovery Environment (Windows RE) and system reset configuration
Windows RE status: Enabled
Windows RE location: \\?\GLOBALROOT\device\harddisk0\partition4\Recovery\WindowsRE
Boot Configuration Data (BCD) identifier: e172b973-f0da-11ed-b413-8dda56e918fb
Recovery image location:
Recovery image index: 0
Custom image location:
Custom image index: 0
REAGENTC.EXE: Operation Successful.
I'm wondering if your information is correct for the layout of your disks.
L.W. (Dan) Danz, Overland Park KS
Reflect v8.1.7847+ on Windows 11 Home 23H2 22631.3085+ | Reflect v8.1.7853+ on Windows 10 Pro 22H2 19045.3996+
Reflect v8.1.7784+ on 2 systems Windows 10 Home 22H2 19045.3803+