External Bootable Drive with Catalina goes to Internet Recovery High Sierra

krislinus wrote:

I did have the “Allow booting from external media” option checked, but still it went into internet recovery High Sierra mode.

I then had to reinstall High Sierra to be able to change the Startup Security settings again and then chose “No security” – only then was I able to boot from my Catalina Install Drive and install it onto my newly erased Macintosh HD drive.

Solved – I don’t know if I am supposed to change the Startup Security Settings back to Full Security now after successful installation though?

Good computing krislinus ! Glad to hear this solved your problem.

If it where my choice I would not re-engage these security options—at the risk of hobbling my own efforts.

If my computer held documents concerning National Security or International Security issues/ Corporate trade secrets— I might have to reflect a moment longer.

krislinus wrote:

The problem is that the Mac will not let me make my Catalina clean install. It boots up in internet recovery and wants to install High Sierra, when trying.

I am unclear what the defaults are set to, however

You could make some changes here:

I see now:

" The default and most secure setting is ”Disallow booting from external media.”

krislinus wrote:

I simply don’t get this:

Im trying to clean install Catalina on my MacBook Pro 2018 15” i9 (T2-chip) but after booting up with Startdisk Manager and choosing my Catalina Install Drive it goes into Internet Recovery and wants to install MacOS High Sierra that came with the Mac...

I understand that the T2-chip makes this procedure more advanced than necessary, but how can I get it to make a simple Clean Install of Catalina?

(Bootable drive created using this guide https://macpaw.com/how-to/clean-install-catalina)

I can not speak to your macpaw link....

You can get the Catalina via the App Store

https://www.apple.com/macos/catalina/

Download Catalina, if it launches automatically quit like any other app.

You can make a USB bootable installer, to make your "clean" install using the Disk Utility.

How to create a bootable installer for macOS - Apple Support

The default T2 chip security settings prevent booting from external drives. You must boot into Recovery Mode and launch the Startup Security Utility located on the "Utilities" menu to allow booting from an external drive.

https://support.apple.com/en-us/HT208198

Do not boot to Recovery.

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