SOLVED: Trouble installing Sierra as Guest in Parallels 14 Mojave Host

I had been delaying an upgrade from Sierra to Mojave because I have a few apps, especially FileMaker 11 and FileMaker 15, that I must continue to run. They would not be compatible with Mojave, so I decided to run them in a Sierra Guest OS. Creating the Sierra Guest OS was way harder than it should have been. Here's how I solved it:

Part A:

1. I started with a clean install of Mojave 10.14.6 on a brand new 3rd party NVMe SSD blade in my MacBook Pro 15" 2015. This works beautifully and is much faster than before.
2. Downloaded the latest version of the Sierra installer from Apple's website: How to get old versions of macOS - Apple Supporthttps://support.apple.com › en-ca
3. The download comes in as InstallOS.dmg. After running it, the Install Sierra app lands in Applications.
4. Tried to make a bootable USB installer for Sierra using the createinstallmedia command in Terminal using Apple's instructions from: How to create a bootable installer for macOS - Apple Supporthttps://support.apple.com › en-ca. I also tried a couple of utilities like DiskMaker but they also failed.
5. The above mentioned Apple site provides the terminal commands for all MacOS versions from El Capitan through Big Sur EXCEPT for Sierra. I eventually found out why (Apple screwed up in 2019 and hasn't fixed the problem yet) from this webpage by brilliant developer Cody Krieger: Creating bootable macOS Sierra installation media on macOS Catalina
6. Cody's Catalina instructions didn't work for me in Mojave so I booted my Mac into Sierra from an external drive and ran just the last 2 of Cody's steps (the first 3 steps are specific to Catalina). This allowed me to successfully create a bootable install volume on a small partition of a USB drive, which BTW gets created WAY faster than on a USB-3 thumb drive.
7. Next, I installed Sierra onto a different USB drive using my new installer. So I knew my installer was good.

Part B:

1. I tried many times to create a new MacOS Sierra Guest in Parallels using my (proven to be good) USB drive installer. Each time, it hung about 2/3 of the way through the process.
2. Someone on this forum had success years ago installing El Capitan as a guest and then downloading the installer inside El Capitan to upgrade to Sierra. I tried that as well many times, but the installation always hung part way through. I even left it overnight once but it didn't budge.
3. Another posting on this forum suggested creating a new hard drive image in the guest OS and using Carbon Copy Cloner to clone a working installation of Sierra onto this new drive image. This I did successfully, then changed the Boot Order of the Guest OS to boot from this new drive image so I could boot into Sierra instead of El Capitan. This also worked. I renamed the Guest OS as Sierra.

Part C:

1. Now that I had what was essentially a clean install of Sierra as a Guest OS, I used Apple's Migration Assistant to bring over just the Applications folder from a clone of my original Sierra drive. I did this because I knew that at least one of those apps would not install directly into Sierra, but would work if brought over this way. This program (FileMaker 11) had been installed in Lion and continued to work as I upgraded my OS over the years. I had tried to install FileMaker 11 in Sierra for someone else in the past and had to install it in Mountain Lion, then upgrade the OS.
2. So after many, many hours (and days!) I have exactly what I was aiming for: a much faster MacBook Pro, a newer Host OS (Mojave) and a pretty quick Guest OS (Sierra). I hope this can save somebody else some time and trouble.