External Bootable Drive will not install IOS

See if you can "Enable Ownership" of the external drive using "Get Info" on the drive:

https://www.makeuseof.com/tag/how-to-unlock-format-external-hard-drive-for-mac

Edit: Also make sure you erased the whole physical drive as GUID partition with either MacOS Extended (Journaled) or APFS (top option) for the file system. Personally I would choose the former if you won't be upgrading this drive later to Catalina which requires APFS.

https://support.apple.com/en-us/HT208496

All your screenshots are showing that you are examining and attempting to install to the High Sierra installer volume which is not an acceptable volume for an OS install. If the external Samsung SSD is not your High Sierra USB installer, then the external SSD may be an aborted install attempt which requires you to properly erase the whole physical drive as GUID partition and APFS (top option) before the installer will accept it as a valid destination.

Snomish wrote:

Yes, I boot the computer to the MacOS Utilities screen. I choose the Reinstall MacOS. When I get past the next 2 screens and it asks which drive, I choose the external hard drive. That is where I run into trouble. I will get a little icon that says that the External HD was locked. I am going try to install it using the USB stick as you suggest and will let you know how that works.

Make sure your external drive is properly partitioned and formatted with Disk Utility as GUID partition and MacOS Extended (Journaled).

https://support.apple.com/en-us/HT208496

What is the exact model of the Mac you are trying to install High Sierra? You can get this information by clicking on the Apple menu and selecting "About this Mac" or entering your serial number here:

https://checkcoverage.apple.com/

The Mac you are installing High Sierra needs to be compatible with High Sierra.

Catalina was installed starting with the 2019 16" MacBook Pro. I don't know what Adobe told you but you cannot run High Sierra or Mojave on yours. One option would be to install High Sierra as a VM in Parallels Desktop, VMWare Fusion or VirtualBox. Depending on which apps you want to run that may or may not be a solution. The other option is to upgrade your Adobe apps.

You have to either disable FileVault, or erase your disk https://support.apple.com/guide/mac-help/turn-off-filevault-encryption-on-mac-mchlp2560/mac

You need to UNCHECK "ignore permissions…" in GetInfo

Not sure if this will resolve your problem, but it's necessary to serve as a boot drive:

Snomish wrote:

I would like to make a bootable external hard drive with High Sierra on it. As it is now, I am following the instructions from Apple https://support.apple.com/en-us/HT201372 to try and create this bootable drive, but I can not figure out how to actually install High Sierra on the external drive. I have the install file on the disk, but have not been able to install it.

Ok, so the process in the Apple support article completed without any errors through Step#7? Can you Option Boot (hold down the Shift key immediately after powering on the Mac) the USB installer as detailed here:

https://support.apple.com/en-us/HT201372#use

and does it boot to an installer screen with about four options listed (Restore from backup, Reinstall macOS, Disk Utility, and ??) ? Most people use a USB stick for the macOS USB installer, but a hard drive can work too.

Do you also have another external USB drive with which will become the actual macOS High Sierra external drive for everyday use which you will use for the 32 bit apps? You cannot install macOS to the same drive as the bootable installer. So to properly install macOS to an external drive you should have the following items:

• Mac with your Catalina install on the built-in SSD (computer must also meet the minimum hardware requirements for High Sierra)
• Bootable USB drive with the macOS High Sierra installer you just created from the Apple article
• Another external drive which will be the destination to receive the full blown macOS High Sierra installation so you can use 32 bit apps.

In the end I may need to install a program called Parallels in order to use my 32 bit programs on my 2020 Macbook Pro that currently runs 64bit Catalina. https://www.parallels.com/blogs/run-32-bit-on-mac/

That is also an option.

In the end, Snomish will not be able to do what he wants even if he managed to install High Sierra on an external drive.

"I am trying to create a bootable external hard drive with High Sierra to use on a New 2020 16" Macbook Pro."

My attempts to explain that seem futile however.

I only see a single Samsung external drive with a copy of the macOS installer on it. Where is the external drive you want to actually install macOS? You cannot erase or install macOS onto the USB installer while booted to that drive.

When creating the macOS USB installer use a USB stick instead of your external hard drive by following the instructions in this Apple article:

https://support.apple.com/en-us/HT201372

When you boot the macOS installer USB stick, then you should be able to erase the physical external Samsung drive as I previously described.

Macs can be picky about the USB sticks used for booting so if a macOS installer USB stick won't boot, then try using a different brand of USB stick since the quality of USB sticks is extremely poor.

Which Mac do you have? You cannot install a version of macOS earlier than what the Mac was originally shipped with.