I am having trouble installing the HiDPI extension to enable retina
In the Security & Privacy, if you are blocked from clicking "Allow" for the HiDPI extension, this is most likely a MacOS / Gatekeeper issue. There are many possible reasons why this won't click, but some things to check for:
Third-party application that emulate mouse or trackpad functions are in-use:
Utilities or applications like MagicPrefs, Synergy, BetterTouchTool, HyperDock, etc., can be blocked from clicking "Allow". Try disabling them and see if there is any differences.
Other methods to try:
- Close Luna Mac app and try to click "Allow"
- Turn off wifi and click "Allow"
- Try a hardware mouse and click "Allow"
Use Safe Mode:
If the hardware mouse didn't work, try is restarting the Mac in Safe Mode,
and access Security & Privacy and see if it clicks from this Mode.
Safe Mode would disable any third-party plugins.
Afterward, restart as normal.
How to restart in Safe Mode:
-Restart your Mac.
-Immediately after you hear the startup sound, press and hold the Shift key.
-Release the Shift key when you see the Apple logo appear on the screen.
To leave safe mode, restart your Mac without pressing any keys during startup.
More on Safe Mode: https://support.apple.com/en-us/HT201262