So are you telling me that if I just upgrade to Sierra, and later decide to upgrade to Catalina or higher, I can't easily take my apps and utilities with me like I normally do when I upgrade, or did I misunderstand?
It would be no harder or easier to install Sierra, High Sierra, Mojave, or Catalina. You would simply install the chosen OS version on your internal drive and all of your existing apps, settings, and data will remain untouched — provided they are compatible with the version of MacOS you are installing.
With Mojave and Catalina you would have the option to use APFS with all of its advantages on your external drive as well as your internal drive. With Sierra and High Sierra APFS is not an option on either your internal or external drive.
If we knew what it was we were doing, it wouldn't be called research, would it?
