I got to a point where all this software was giving me those “you shall not pass” thing because my OS is too old. I hate that Apple forces this issue now by the way… I’m still running Mavericks because it meets most of my software needs… I put my test partition on High Sierra… Whoops… But no not really, it doesn’t even ask you if you want to update your hard drive to the latest file system it just goes ahead and does it.
Now I have to find a spare USB so I can undo that because I have no need for High Sierra on my 2011 MacBook Pro. I mean… they’re even asking me to upgrade to Mojave, which I’m almost sure I can’t do without a graphics card that supports Metal.