I have an HP Elitedesk 800 G1 SF (Product No. C8N26AV) that I recently purchased from the local surplus shop that I would like to set up as a Linux machine. The hard drive was removed and I've put in a new SSD (easier to find these days than HDD). I'm using a 2011 MacBook Pro with High Sierra 10.13.6 to download the OS to a USB drive which I will use to boot the HP. Everything looks good on the USB stick and the HP's BIOS so far but when I go to boot (Esc, arrow down to Boot Menu, arrow to USB) I get a blank screen with an underscore (or minus) in the upper left corner. The OS I'm trying to use is Lubuntu 20.04.1 LTS.
More detail on what I've tried so far:
Downloaded .iso file from https://lubuntu.me/downloads/
Followed this guide to make bootable USB stick: https://ubuntu.com/tutorials/create-a-usb-stick-on-macos#7-boot-your-mac. (In sum, erased USB stick, ran belenaEtcher.) It looks like I did this properly since I can use this to boot on my mac, though possibly the guide I used was specific to a mac target computer? That seems unlikely as there weren't many branch points, although I did try formatting the USB using both GUID Partition Map and Master Boot Record, with the same results.
Insert USB stick to the HP, turn on, hit Esc key to go to Boot Menu, then select USB. The system at least recognizes that there is a USB present since there is no USB option when I boot without it. Then I get a blank screen with a static underscore (or minus sign) in the upper left corner.
I also ran the memory and (quick) hard drive tests and those passed. For now I am avoiding modifying the BIOS since it looks like it's working properly, but if necessary it looks like that's what I'll have to try next. The computer has a blank hard drive and no web connection yet so I would have to go through the USB on my Mac.
Anything I could be missing to figure this out? Is this a BIOS issue? Any help would be greatly appreciated.