Re: Booting from thumbdrive...

I'm confused by the cumulative presentation of the information, so I'll 
dump what I know that might be relevant.  And some that isn't.

Because something has gone wrong, I recommend that you double-check all 
kinds of assumptions.

- Not all ISOs can be dd'ed to a thumb drive and booted.  That involves 
  tricks that various distros have adopted at different rates.

  test: Can you boot this particular USB, as it is now, on another system 
  in legacy mode?

- I've had systems where booting into Windows (accidentally, due to typing 
  F12 too slowly) with a Linux installation USB plugged in, actually 
  screwed up the contents of the USB.  It was repeatable.  Horrible.
  I blame Windows.

  Suggestion: see if your USB content is exactly what you put there
  (cmp instead of dd).

- does the Linux on the USB have a self-check option?  One that verifies 
  the contents of the USB?  (Fedora does and I find that very useful and 
  comforting.)  If so, try going through the self-check of this USB on 
  a machine that is willing to boot it.

- in the firmware setup screen of your ThinkPad T450 (it is not a BIOS!)
  check to see if you have disabled booting from the USB port.  I'm pretty 
  sure that there is at least one or more options with this effect.  It's 
  considered a security feature.

- Is Windows booting in UEFI or Legacy mode?  All systems installed on a 
  disk should boot in the same mode.  Given a choice, I actually prefer 
  UEFI to Legacy.  Each regime has quirks/stupidities.

- in the firmware setup, have you enabled CSM?  You need it.  I would hope 
  that it would automatically be enabled with Legacy Mode, but it is worth 
  a check.

- I (mostly and frequently) install Fedora.  They've got booting from a 
  USB stick down well.  Consider downloading it and trying to boot it as a 
  live system (without installing).

  That's a lot of work for a small test but you've been struggling with 
  this problem for a while.  Bonus: a USB with a bootable live Linux is
  useful in a number of recovery situations.

- can Windows see (not read) the flash drive?

- have you tried a different USB port?

- some firmware systems don't offer a boot choice if they don't see 
  something bootable on that device.  This may only apply to UEFI since it 
  isn't really possible to make that determination for Legacy mode.  
  (UEFI requires at least a populated ESP (EFI System Partition with a FAT 
  filesystem.)

Do tell us what you find.

Good luck!
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