Unable to install iTunes 12.6.3 on macOS High Sierra 10.13.6

***This is a resolution, not a question.***

After hours of trying and failing, I finally was able to get the work around to get iTunes 12.6.3 version working with functional access to the app store on a revert to macOS High Sierra 10.13.6

Background:

I decided to do a hardware upgrade & software roll-back to my Macbook Pro 13", cir. 2012.

I was running macOS Catalina, but wanted to return to operating 32-bit apps & also wanted a version of iTunes with an internal app-store to manage old apps.

Problems:

-In rolling back the software, I decided on macOS High Sierra 10.13.6 after attempting to us macOS Mojave only to discover it could not/would not run iTunes 12.6.3.

-After rolling back to macOS High Sierra, I then faced problems installing iTunes 12.6.3, with two error message when attempting to install. The first, which was overridable as admin, stated that the certificate had expired (IMPORTANT). The second, which resulted in installation failure, stating that this version of iTunes was "not compatible" with my macOS. This was extremely frustrating, as I was only able to find online information suggesting they were compatible.

-After fiddling around, I found the thread here on this forum suggesting to "roll the system clock back" to trick the system into allowing download after expiration. My download of iTunes 12.6.3 referenced the certificate expiration to 2019, so I changed my system time to reflect calendar year 2018, which worked (THERE IS MORE, DO NOT STOP HERE).

- Still, upon opening the iTunes App, I did receive the following error message:

The File "iTunes Library.itl" cannot be read because it was created by a newer version of iTunes. Would you like to download iTunes now?

>>> "Quit" or "Download"

-If you make it here, this video helps immensely:

https://www.youtube.com/watch?v=C9C107nYxSc

In the event that the video gets taken down, essentially, it is telling you to:

1. Select "Quit"
2. Open Finder>user(house icon, "name of user")>Music>iTunes>Previous iTunes Libraries
3. *You Must* select a library dated 2017 or earlier. I don't know why, but it did not work until I selected a library version created 2017?
4. Duplicate this Previous Library (2017) into the iTunes folder (essentially, one folder outward)
5. Rename the file in iTunes folder labled "iTunes Library.itl" to reflect "iTunes Library (TODAYS DATE).itl"
6. Rename the Previous Library file that you moved to reflect "iTunes Library.itl"
7. Now, RESET YOUR SYSTEM CLOCK to reflect the current calendar year.
8. Try opening iTunes. It should be version 12.6.3 and you should be able to access the appstore no issue with an Apple ID.

Hope it helps,

M