76 here.

There are only TWO (top level) folders to copy ENTIRE CONTENTS over
Here is how I would do it:
STOP if anything fails (avoid making it worse and come back with the messages for help)
1) Install Calibre on the PC (Latest release that works for your OS version).

The typical W10 install is
Code:
C:\Users\yourlogonhere\Calibre Library

If it is NOT then you will need to Run Calibre, there should be only 1 book (the users guide by John): highlight that, Tap 'O'.
This opens the location. Go back 1 level, you should see just the files in the image.
DO NOT do more if you see others you care about. they will be lost
2) Delete those.
Remember the PATH to this folder. Exit Calibre (PC)
3)Using the OS browse to the Portable drive (see image:drive letter may be different), Open the Calibre Library folder: select ALL (ctrl-A):right-click:COPY:
Switch to the NEW/ Empty LIBRARY: Right-click: PASTE ... and let it grind (takes a bit of time for larger libraries, so grab a cuppa)
STOP if anything fails (avoid making it worse and come back with the messages for help)
OK, time to copy your User SETTINGS (AKA Configuration)
Open the
Calibre Settings folder on the USB drive: Select
all: COPY
Switch to your new drive
Like before,

the default is
Code:
C:\Users\yourlogonhere\AppData\Roaming\calibre
PASTE (OVERWRITE all if asked)
Last step: Start (new) Calibre: It might complain that xyz Library is not found and it will use... (should use the one you copied if default location) and you are good to go