Apple - macOS cannot connect to OpenVPN using Shimo - Kext error
After contacting their support they responded with the following which solved the problem.
When this happens open the System Preferences and go to the Security & Privacy settings panel. On the General tab, at the bottom right corner, there should be a message, saying that the use of system software was blocked with an Allow button next to it. After clicking on allow, there should be a dialogue to allow the use of software signed by Fabian Jaeger. If you don't see such a message do this alternatively:
- Go to this page: http://tuntaposx.sourceforge.net/download.xhtml and download the tun/tap kernel extensions
- Install the package, you have to quit Shimo and other VPN clients you might be using before doing so
- Go to this folder: /Library/Extensions
- There locate the tun.kext and tap.kext file and copy them
- Go to your Applications folder, find Shimo, right-click on it and select Show content package
- Go to the folder Contents/Ressources/tuntap
- Paste the previously copied files inside the tuntap folder and override the existing ones there
- Reboot your Mac and try to connect again with Shimo
For what it's worth. I had this issue on Mojave, and in the end, rebooting simply made it work without reinstalling tuntap.