Option 2 in the Windows Repair program can snag Environment Variables and repair sometimes, but because Win 10 was changing so much, it was difficult to keep up with all of the files that would need finding and manually uploading.
That is why the Cat & Mum File requests section has been closed.
While some problems can be resolved with an upgrade, sometimes you can take the problems with you so I think it's best to sort them before an upgrade.
When the time comes, you can use the Assistive Technologies link to free upgrade to Win 10 and as long as you don't remove the Windows.old folder, you should still be able to revert within the 30 days if still problematic.
I suppose you could give it a try to see if it resolves your problem, but fully disable or uninstall your AV program first with its Uninstaller.
Sometime the install can stick on the busy after the 74% reboot and you have to power shutdown then reboot.
If this continues to happen then keep shutting down/reboot and it will either recover the installation and complete the install or will revert to the previous OS.
https://www.microsoft.com/en-gb/accessibility/windows10upgradeI upgraded a Win 7 laptop to 10 in October, although I don't know how much longer it will remain active for.
Prior to upgrading two OEM Win 7 laptops, I created the Recovery disks and created a Windows System image onto a spare external HDD as well as creating a System Repair disk, but I haven't had to use those.
It's advisable to go into the BIOS and change the Boot order to check the DVD and USB drives before the SSD/HDD as the F keys no longer function for those options in Win 10, although there is a bcdedit command you can use to change the boot to legacy and you need to disable fast start.
NB - I see from your recent post that you have found Option 2.