Yeah, it seems that there is a lot of issues with the "Allow" button in High Sierra :/
According to what I've read on Apple forums, if you have 3rd-party software that can intercept and/or emulate your mouse movements and clicks, you will not be able to click on the "Allow" button.
Here's some threads I've found:
- Allow button doesn't work in Security & Privacy
- "Allow" Button in System Preferences for Blocked System Software Doesn't Work
I've also read that using Wacom tablets might also cause the issue, so if you unplug your Wacom, then click with your normal mouse on the button, it might work.
There's a lot of info on this page: https://github.com/tekezo/Karabiner-Ele ... ssues/1017
I had a similar issue in 10.13.3. It took a few days to find a fix. Namely, Security asked me to "approve" Google for its Google File Stream Drive KEXT. In console, I could see that the keypress event was being rejected. It was ultimately due to the use of a third-party mouse from Logitech. I plugged in my Magic Mouse, click on the "approve" and things started to work as advertised.
So, I figured this out!!! I use magic perf to intercept various touchpad actions. It seems like Apple is obsessed with security. If you have this problem try to disable any apps that my capture and forward clicks. The click must come from the touchpad directly. << pulling my hair out >>
Alternatively you can use the keyboard, if you have full keyboard access enabled:
Then just press tab several times until the "Allow" button is highlighted, then press space to activate it.
Can you try these solutions, and if one works, tell me which one ?