Sorry, my mistake! I mean
chkdsk D: /check

You don't have to find any osdevice! It's (D:)
I believe that the Recovery boots from (E:)

Whith a corrupt BCD it would not be possible to to boot...

All that is confusing.
Usually you get a manual with the equipment you buy.
Usually you can save/export the settings and re-import the settings. If not make a photo.

save/export settings
Unplug...

That is wrong! And as long as you are playing you make it worse. When I read TrustedInstaller etc. you ruin everything!
PE doesn't support WiFi and as long as you are working without LAN, you will...

Create a screenshot and add like here:

Boot into Recovery and run
X:\Windows\System32>sfc /scannow /offbootdir=D:\ /offwindir=D:\Windows /offlogfile=D:\sfc.txt

It's better to post a "Diskmanagement" Screenshot showing both disks before you do anything

Only if it's not on (C:) ==> Step 2

It was on C :\Windows\System32\Recovery ! Why did you run Step 2 commands?

410214

You should find these 2 files in the Recovery Folder

Then type...

"... clone ALL the data in both HD's into two seperate files".
Files or Folders ?

Go to the X:> prompt and type:
diskpart
sel disk 0
list par
sel disk 1
list par
exit
bcdedit

post result

!!!!!!!!!!! Delete that 1903 Version !!!!!!!!! That creates so many problems afterwords!!!

You can use that MajorGeeks instruction for the USB
Select Create installation media (USB ....) for...

If you shrink the size by 1627819 the final C-Partition size will be 279329 MB = 272 GB That is more than enough
So you just click on "Shrink"

I would shrink to 280 GB. That means enter 1620428...

When you unplug the Router you have to wait for ~3 minutes before you plug in again!

1. Your MB supports UEFI and supports Instant Flash
2. last BIOS Version is 1.60 (2016)

3. Rightclick in Diskmanagement on (C:) and select "Shrink Volume" and make a Screenshot of that window....

Find the WinRE.wim
1.
dir /a /s c:\Windows\System32\winre.wim

Only if it's not on (C:) ==>
2.
diskpart
sel disk 0
sel par 4
assign letter=R

When you are in RE-Command Prompt you can run the setup also from USB.

Example USB Drive letter (K:)

in X:> type pushd K:
K:> setup.exe

The update to 3920 was successful.

reagentc /enable
wait 10 seconds
reagentc /info

You don't need any USB-Disk to install an OS.
1. Create a Partition for the 2 nd OS.
2. Make sure that the Recovery Environment is working and boot into Command Prompt.
3. Map a network-drive...

It's so easy to explore the contents of a *.vhdx that you must have made s.th. wrong.

Did you have an internet connection when you executed the dism-command without /source?
Did you ever run:
DISM /Online /Cleanup-Image /StartComponentCleanup

use cmd (admin) instead of PS

to...

Did you assign a Drive Letter? Then you should be able to see the files in Explorer.

run cmd
reagentc /info

Bitlocker! turn it off first :redcarded:

C:\WINDOWS\system32>reg query "HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion" /t REG_SZ /v WinREVersion
...

And (J:) is the mounted path of the ISO?
I would copy the install.wim to a folder like C:\Install

But your source file is here:
J:\CCCOMA_X64FRE_EN-US_DV9\sources\install.wim
and not
Source:J:\sources\install.wim

:-)

When you run Windows Update you can check the success by this command:
Dism /Get-ImageInfo /ImageFile:\\?\GLOBALROOT\device\harddisk0\partition4\Recovery\WindowsRE\winre.wim /index:1

The...

Did you see the install.wim in the source-folder?
Is the ISO from a Media Creation Tool?