I'll offer you another path forward for the '32-bit issue'. I need that USB key so I can use it on both my iMac and my Macbook Pro, so that I can boot into High Sierra or Mojave and where I can install the apps I need for work, without needing my internal drive.' 'Basically, I need a USB key with either High Sierra or Mojave on it in order for me to keep working with 32 bit apps I need for work, since I want to upgrade my main drive to Catalina when it comes out. Only thing I can think of is that there may be a problem with my Toshiba USB3 flash drive, but it seems to work just fine when I used it for other stuff. Left this one for 2 hours as well, but it just won't finish. Unfortunately, it just stops at the same moment, with 14 minutes left (sometimes switches to 13 minutes).

I tried it this way because I thought the problem might be that my USB2 key is too slow. I then wiped my Time Machine partition on the external 2Tb USB3 HDD (because I want to switch from a local TM backup to a networked one, connecting the drive directly to my router instead of the iMac, and local and networked TM backups are apparently not compatible) I put the High Sierra installer on the newly created partition and booted up the installer, no problem. Tried it on the iMac and on the Macbook Pro. I left it there for over 2 hours, and nothing happens. The installer boots up just fine, but gets stuck halfway (not frozen, because when typing CMD-L, it says installation in progress). I've tried with 2 USB keys, one USB2 with 8Gb which I used to create the installer, and the other USB3 128Gb key to install High Sierra on. I also have a mid 2015 15 inch Macbook Pro, which had Yosemite as the original OS. My iMac is a mid 2017 27 inch model, came with High Sierra installed.

How to install high sierra on usb