Can't click Allow when System Extension Blocked

If clicking the Allow button does not work when trying to enable a System Extension, try this:

1. Open Keyboard System Preferences.
2. Enable Full Keyboard Access (All Controls) on the Shortcuts tab.
3. Open Security & Privacy System Preferences.
4. Use the tab key to highlight (outline) the Allow button.
5. Tap the spacebar to activate the Allow button.

Note: I found this in a post several months ago (perhaps a year). However, I haven't been able to find that post again. If someone know where it originated, post the link in a reply here and I'll link to them for credit.