HI ScerboReggie-7037,
0.Could you please enter winver in command prompt on win10 1607 computer and look the os version and os version number? Is it win10 pro/enterprise 1607 or win10 enterprise 1607 LTSC?
1."I've heard Update Assistant can drop some settings and configurations. I cannot lose these files."
Yes, I also hear that.
If we worry about lost something, I think we can try to do system image backup and file backup for one test PC first, then try to in-place upgrade from win10 1607 to windows 10 higher version, finally we can check the same issue also happen on our environment.
We can try to do system image backup before we do in-place upgrade to high win10 version。
How to Create a System Image Backup in Windows 10
https://www.youtube.com/watch?v=rtPrM3-k0jQ
Backup files before new computers and Windows 10 upgrades
https://www.youtube.com/watch?v=5t0hD4WxLIc
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2.If we upgrade to Windows 10 version 20H2 using ISO File from Previous Versions of Windows 10, will there be "keep personal files and apps" option we can select?
How to Upgrade to Windows 10 version 20H2 using ISO File from Previous Versions of Windows 10
https://answers.microsoft.com/en-us/windows/forum/all/how-to-upgrade-to-windows-10-version-20h2-using/617a37da-8fc0-4f33-a3eb-59fe9082f925
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