I don’t know what to say. I am out of ideas. It really should not be that hard really.
From your past experience, that seems to be the case as well.
Something is up with the BIOS/UEFI maybe. Check to see if there is a firmware upgrade?
If not, reset the BIOS/UEFI to factory!?
I don’t think that I can help your past that. Most sane systems do not mount an ISO at boot from thumb drive.
My recommendation when installing a linux iso to a usb drive is dd or on windows rufus and you have etcher that work on both windows and linux.
If you are trying to recover a broken ubuntu or debian system use debootstrap to chroot in to the system to fix it or to retrieve data.
Here is my way to dd a iso image on linux dd if=/home/habbis/Downloads/Fedora-Workstation-netinst-x86_64-27-1.6.iso of=/dev/sda bs=4M status=progress && sync