Back finally

- let's clear up GParted a bit, then I'll get onto that Summary.
If any of the following is too tricky, that's cool, and we can revert to using GParted from one of your install sticks, 18.3 or 19.
I'll start at the end (works for me

) and the screenshots are from my rig, yours will differ, but have similarities, if you follow me.
SCREENSHOT 1 - ENTRY TO GPARTED LIVE
This is the sort of screen you will find, and the highlighted entry is where we enter.
How are you with Bluetooth, or with connecting a cable from your mobile phone (cell phone) to your computer?
If you can take a couple of pics of your Setup Utility options BIOS screens), that would be cool.
I'll show you a few of mine. With the B&W screens, I use the highlighted entry as a pointer, you may not be able to read the text, I'll call it "the white bar".
SCREENSHOT 2 - WIZARD'S 1-TIME-BOOT SETUP SCREEN (ACCESSED FROM MY F12 FUNCTION KEY)
Above the white bar - USB storage device is actually where I have to enter to get up GParted Live when it is plugged in. Even though my computer is UEFI, I have to use this Legacy (aka CSM - Compatibility Support Module, under Windows) (aka BIOS) option ... go figure
Down under UEFI Boot: we have some of my Linuxes, and my Western Digital My Book 4TB powered External HDD, connected by USB port. We'll see that again, soon.
SCREENSHOT 3 - SAME AS ABOVE, BUT WITH A LINUX INSTALL (LIVE USB) STICK INSERTED
If I don't have my Setup Utility set to boot from USB first, before the HDD, I go in via my one-time boot key F12, below the white bar (debian) is still my Western Digital, but below
that is my Live stick, for, say your Linux Mint 18 or 19. And that is where I would enter to install or test Linux.
In Other Options: is BIOS setup (technically confusing, it covers BIOS and UEFI, but I won't go there), and that is where we are headed next
SCREENSHOT 4 - WIZ'S MAIN SETUP - FEATURES BOOT SEQUENCE
I can access this screen and its optional pages/tabs, from two directions (3 really, counting my Grub Menu, another time on that).
Using F12, through the black and white screen, I can choose Other Options: BIOS Setup, or at bootup, I can hit my F2 button.
You likely have two (2) buttons as well, quite often they are F2, F10, F12, or Delete, and 2 will work in slightly different manners.
So I came in with it at Settings, and once I choose General - Boot Sequence, we see the grey part on the right.
There, I can choose between Legacy and UEFI to run under. If your Speccy info was correct (don't doubt
you) you may not have any of the UEFI stuff above, OK?
Have a go and see if you can access that GParted Live stick, and if not, we can revert to using one of the sticks you used for Linux Mint 18 and 19.
Gotta 600 kilometre round road trip tomorrow, so back after a day to work on that Summary.
Cheers
Chris