Windows 10 DISM cannot find files, even with ISO mounted

Finally solved it. As I could find out here Windows 10 DISM error: 0x800f081f the ISO created by the Windows 10 Media Creation tool does not work with DISM. I downloaded one from Techbench and managed to use DISM with that one.

I do not know whether it is the fact that the ISO created by the Tool has an ESD file instead of a WIM one, but changing the ISO to the Techbench one (which uses a WIM file instead) and using the adapted command DISM /Online /Cleanup-Image /RestoreHealth /Source:WIM:G:\sources\install.wim:1 did the trick

I cannot accept my own answer for 2 days, so will have to wait to mark this as answered

So, I was having the same problem, and I was able to solve it using the following method.
I downloaded the Windows Image (ISO) using the Microsoft website. Therefore, I did not want to download another image using a third party website.

To solve this, try following these steps.

• Download the Windows Image
• Extract it to a Local Drive. (For example E:/)
• Make sure it has all the necessary permissions.
• Make sure your command is correct. (E.g.: Drive Letter, Index number, etc)
• Try it now.

If it doesn't work, create a new administrator account and try again.  

Commands:

• SFC /SCANNOW
• DISM /Get-WimInfo /WimFile:G:\WinISO\sources\install.wim
• DISM /Online /Cleanup-Image /RestoreHealth /source:WIM:X:\WinISO\sources\install.wim:1 /LimitAccess

To check the index number, run this command.
DISM /Get-WimInfo /WimFile:X:\WinISO\sources\install.wim
( 'X:\WinISO\sources\install.wim' - This should be replaced)

If you are not certain about the commands, please check these websites.

• https://support.microsoft.com/en-us/help/929833/use-the-system-file-checker-tool-to-repair-missing-or-corrupted-system
• https://www.wintips.org/fix-dism-source-files-could-not-be-found-windows-10-8/
• Windows 10 DISM error: 0x800f081f

Download Microsoft Windows:

• https://www.microsoft.com/en-us/software-download/windows10
• https://www.microsoft.com/en-us/software-download/windows8ISO

If you are having trouble downloading Windows ISO from Microsoft website, please refer to these websites:

• https://www.howtogeek.com/427223/how-to-download-a-windows-10-iso-without-the-media-creation-tool/
• https://www.itechtics.com/windows-10-download-iso/