To JoeMike: I am going to paste your last post to me regarding adding Catalina to my Mac. I will interject in green. I haven't done any of the real actions yet, but I did go through step-by-step and look at some things which gave me some questions.
Given you have a bootable copy of Sierra on your external drive we can shortcut the process.
PLEASE, PLEASE, PLEASE DO NOT GET AHEAD OF ME.
FOLLOW EACH AND EVERY ONE OF THE FOLLOWING STEPS IN EXACT SEQUENCE
I BOOT FROM THE EXTERNAL CLONE
1 Attach your external drive to your computer
2 While booted from the internal drive on your computer,
3 Verify you have SuperDuper installed on the external drive I do
4 if possible verify the missing files are on the external drive They are
5 go to System Preferences > Startup Disk
6 Select the Sierra 2015 as the boot drive
7 Click on Restart (When this completes you should be booted from Sierra on the external drive)
II PREPARE THE INTERNAL DRIVE
1 Open Disk Utility
2 in the Disk Utility sidebar, select the internal drive DRIVE (Be sure you select the physical drive not one of the paartitions on the drive) I am assuming you mean click on the drive called Apple SSD because below that and indented is Mac HD and then Mojave and Catalina.
3 On the Disk Utility tool bar select Erase (It's grayed out) then Name: Macintosh HD, Format Mac OS Extended (Journaled), Scheme: GUID Partition Map
4 Click Erase (again?)(This will effectively erase all content on your internal drive and all partitions) (Again, it's grayed out)
III CLONE SIERRA BACK TO THE INTERNAL DRIVE
• I don't have SuperDuper as an exemplar but I believe you know how to use it correctly. Your target drive is labeled Macintosh HD (I don't know how to do this. Can I skip this step? I probably won't be using Sierra again anyway except on my older mac.)
IV BOOT FROM THE INTERNAL DRIVE
1 While booted from the external drive go to System Preferences > Startup Disk
2 Select Macintosh HD as the boot drive (You mean Apple SSD which is above the Mac HD in the list?)
3 Click on Restart (when this completes you should be running Sierra from the internal drive on your computer and have a full 120GB available storage)
4 If your missing files were on the eternal drive they will now e on your internal drive. If not, you should have had a backup system like Time Machine running regularly.
V IF YOU WISH TO UPGRADE TO CATALINA
1 Open App Store
2 Search for Catalina
3 Click on Get
4 Follow the on-screen instructions.
5 Your computer screen will go blank several times and there will be excruciatingly long pauses but after 45 minutes or so...
6 You will be prompted for your logon password and you will be running Catalina
a There will be a new folder on your desktop that you can ignore
b Your internal drive will have been converted to APFS and there will be four APFS volumes on your internal drive (all showing a capacity of 120GB -- I will explain what is going on if you are interested)
c As time goes on, you will find you need to approve all sorts of things as part of Catalina's increased security precautions
d You will need to immediately update OnyX, SuperSuper, and probably a few other applications.
e You will have entered the 21st century of Apple computing
f If you switch to Carbon Copy Cloner you can turn on APFS Snapshots which will provide some limited protection against inadvertent file loss. (I tried CCC in the past and found it confusing, so I will stick with SuperDuper.)
If there are any major steps I can avoid because I am not going to use Sierra, let me know. Thanks for all your time, JoeMike. I appreciate it.
