This is the same ISO that booted and installed on the two desktop systems. On the off chance it was the 2nd drive with Win 10 causing issues, I removed it from the bus: nada.
The bios screen flashes by into darkness, with this message: Boot Error.
What, if any, is the word on the bitline?
Did you disable secure boot and then enable Legacy?
Legacy is enabled, and this bios has no secure boot, so no joy.
What ASUS laptop model that you use?
It’s a UJ-30JC. Very well taken care of… 
I just saw that Akito had a similar issue with usb ports on his notebook a year or so ago. He was able to put the ISO onto an NMe drive and booted from it to get it operable. I actually have a new NMe drive…so the gears are turning! We shall see.
Seems like people are reading my posts, after all.
You remember correctly. However, you could do that “trick” I did with any second storage medium. May it be a hard drive or SSD, it does not matter. It just matters, that this device can be easily removed from the laptop and be put in again. Then you can pretty much use it like a pseudo USB drive.
Yes! I realized that I also had a 250 Gb ssd that would simplfy the process: just put it in the notebook. I will report back 
I learning all about adding menuentry to grub via /etc/grub.d/40_custom 
Back later…
Some systems I have run into over the years have issues with USB ports. The “U” gets a little gray sometimes even when built into the same box. That issue continues to fade into rarity, Thank goodness.
Well, I tired of trying to to grok menuentry via /etc/grub.d/40_custom…But, as I write, 20.04 is finishing up its install on my ASUS notebook 
I had transferred the ISO over my local network to the notebook while still pursuing the menuentry path. After I gave up, I decided to use an older 2.0 usb stick instead of the 3.0 usb sticks; I put the 2.0 into the usb port on the notebook and used the “Startup Disc Creator” from the Ubuntu menu on my desktop to make a bootable usb drive. After the process was finished, without ever removing the usb drive, I rebooted the machine and set the notebook to boot from the usb drive. Which it did! The older ASUS notebook had no problem with the 2.0 usb drive as a boot drive, despite rejecting the 3.0 usb’s as boot drives. I guess the old dog didn’t want to learn new tricks!
Abhishek’s reply to another question was what gave me the whack on the head…Got the lateral thinking back in the groove!