Here are your partitions...
Local Disk is the name of your 1909 partition. It is C: when you boot to it. Otherwise, it's D:.
Windows is the name of your 1809 partition. It is C: when you boot to it.
Otherwise, it's D:.
Recovery Image is your old D:. It's been pushed to E:.
Soon, we want to delete all of your partitions & redo the clean install. Then you will have EFI, MSR, Windows (C:), & Recovery -- all of it belonging to 1909. I'm satisfied your computer can take 1909 because DISM, SFC & Windows system image all worked.
Are you satisfied yet that your apps will work in 1909? Then let us proceed to the next step. We have to nuke it all & redo the clean install.
No wonder the image took so long to make. It included both 1809 (D:) & 1909 (C:). Did it offer E: too & did you select it? Then it's got Win 8.1 too.
(1) Let's rename the image to keep it separate & distinct from the next one...
(a) Plug in the external HDD that holds the image.
(b) Open the WindowsImageBackup folder on it.
You'll see one folder inside with the name of your computer on it.
(c) Append "-1909_with_1809" to its name.
That's the name you'll see, if/when you must restore that image. The next time you make an image, append something to its name too. I delete the oldest one before making a new one, so that I always have three...

(2) OK, let's practice how to restore it. Boot to any recovery environment. If the computer is completely dysfunctional, you'll still be able to get to the one on your 1909 Installation USB drive.
(a) Plug in both the Installation USB & the HDD that holds the image, then reboot.
Or, maybe wait till after (d) to plug in the HDD, in case they can't be told apart.
(b) Immediately press ESC repeatedly for the Startup Menu.
(c) Press F9 at that screen for the "Boot Device Options" screen.
(d) Select the 1909 USB Installation drive to boot to it.
(e) Click "Repair your computer" instead of to install.
This will reboot to the recovery environment.
(f) Then "Troubleshoot > Advanced Options > System Image Recovery" will start the process.
Do it to see that your image will be offered. But back out as soon as you see it.
Don't do a system image recovery until it is necessary. It will restore all the partitions it contains back to where they were at the time the image was made.