11. Apple could not verify the installer. How to open the installer.

MacOS Gatekeeper preventing the opening of the .pkg installer. This is a common issue on modern MacOS.

Open System Settings > Privacy & Security.
Scroll down to the section that says:
“MPH_MAC_INSTALLER-...pkg was blocked from use because it is not from an identified developer.”
Click “Allow Anyway.”
Then, right-click the .pkg file and select “Open.”
A new prompt will appear — this time with the option to “Open”. Click it.