Cannot allow HoRNDIS kext in Security & Privacy pane

[mikhailai]

Thanks to @dudymas for finding this solution:

My own issue was that when I clicked the 'Allow' button for the kext in the Security & Privacy pane, the Allow button wouldn't go away and nothing seemed to happen. Reading around, I found a related issue with another kext: tekezo/Karabiner-Elements#1017

With the knowledge there, I turned on Full Keyboard access from the keyboard pref pane, and then I went back to the allow button, and used the Tab key on my keyboard to highlight it, then pressed the spacebar to 'allow'. The button went away, and suddenly my usb tethering was working without issue.