I just wanted to give a heads up that it would be very worthwhile to add a bit of additional information at step “step 6 is going into System Preferences > Sound and choosing IShowU Audio Capture” which is that there’s a caveat for macs running OS 10.13 or later (High Sierra/Mojave), because there are reports that using a Wacom or even a Magic Mouse with some settings enabled will actually prevent your clicks on the “allow” in your security settings from working. I was in fact using my trackpad and found that no matter how many times I clicked “allow” it would just flash and stay put, so I found this page on iShowU’s help site which straightened everything out: https://support.shinywhitebox.com/hc/en-us/articles/360003524192-iShowU-Audio-Capture-not-showing-up
turns out multiple reboots were needed in my case because there were a few KEXTs queued up from earlier, so please don’t discount needing to reboot, it’s not just BS, you really do need to reboot to install the KEXT.