Software to create a macOS boot installer

https://diskmakerx.com/ supports earlier OSes than Big Sur.

Create a bootable installer for macOS - Apple Support

Is Apple's directions for other methods of doing it.

Generally you can only do this on a system that is as old as the OS in question, and only with installers that will run on the system in question creating the OS. If your Mac is running a newer OS, than why you are trying to create, and is compatible with the older OS, use internet recovery to install an older OS on a separate partition first, and then create the installer.

Take a look at open source TINU. It provides a GUI interface to create macOS installers.

Note, I have never used it myself, so I cannot comment on how well it works.

What is the exact model of your Mac and current version of macOS being used? You can get this information by clicking the Apple menu and selecting "About This Mac".

What version of macOS are you trying to install?

And do you have the full macOS installer? Was this downloaded directly from Apple even if it involved a third party app such as the one mentioned by @MartinR? Some third party utilities such as the one mentioned by @MartinR may actually download the installer directly from Apple's own servers. I am only familiar with the installers acquired directly from Apple. If you have such an installer, then I may be able to provide instructions for creating a bootable macOS installer recovery mode USB stick....that is it will act like booting into Recovery Mode so it will then download the installer from Apple's servers.

Why are you trying to make a bootable USB installer? You stated that both Sonoma and Ventura are installed. Run the installer that you downloaded and tell it to install on the external drive.

If you tried that and it failed, creating a bootable USB installer won’t change anything.

Tom Wolsky wrote:

I know you can create a boot installer using a complex Terminal string. I was wondering if anyone knows of an application that will do this for you, software that will take an OS installer package and create a boot installer on a flash drive.

Thanks very much.

Maybe it’s complex, maybe it’s not, but all you have to do is copy and paste. Just name your thumb drive “MyVolume,” copy, paste, hit return. I have no idea why that requires any more of a GUI than provided in Terminal.

My installer app has none of the names listed by Apple.

Then you don’t have any capability to create a bootable installer.

If I fully understand your reply, a full installer version is not often available for at least a month.

FYI, if you have an M-series Mac, then you will only be able to create a bootable macOS USB installer for macOS 11.x+ since only an OS installer compatible with an M-series Mac will be allowed by the "createinstallmedia" utility, so any third party app which also uses the"createinstallmedia" utility will have the same limitation.

If you can acquire the full macOS installer from Apple, then there may be other methods to create a bootable macOS USB installer....or at least a bootable macOS Recovery Mode USB boot disk installer.

This is from my own personal experience.

Tom Wolsky wrote:

I’m using an M1 MBP. I have the current versions of Sonoma and Ventura internally.

At this point I’m at a loss why I can install on an external drive. I’ll try a test with an Apple Sonoma install from the Ventura volume.

AFAIK, You cannot run the Ventura installer while booted from Sonoma since the Ventura installer recognizes you are currently running a more recent version of macOS & sees no need for it. Apple doesn't consider the possibility someone would want to create another bootable macOS volume or drive for an older version of macOS. Apple only looks forward.

I don't think I've tried to install macOS to an external drive while running the installer from within macOS itself for an M-series Mac. I do know that when booted into a macOS USB or online installer on an M-series Mac that you are prompted to assign ownership to the new bootable OS volume prior to installing macOS onto it. I don't know if Apple ever considered this need when running the macOS installer while currently booted into macOS.

I've only personally created two external macOS boot drives for the M-series Macs so my experience in this area of M-series Macs is limited. I used a bootable macOS installer both times.

Tom Wolsky wrote:

I tried running the boot installer from a jump drive onto an external drive. The system seems to load but after the installation it never starts up in the new install. I never get Hello. Instead it boots into the original OS, and the new external drive cannot be assigned as the startup disk.

Actually this can happen even on Intel Macs where instead of booting into the new installation, it will just boot to the internal drive. Try booting to the Option boot screen by holding the power button down while powering on the M-series Mac to access the Startup Options screen. See if the external boot drive is seen as a boot option....if so, then select it to see if it will complete installation or allow you to finish setting up the new OS.

Tom Wolsky wrote:

When the installation "completes" the system doesn't boot into it, but into the original drive. The newly installed "system" is recognized as a system in Startup Disk, and is selectable. But when I click Restart it fails with an error that the system has to be reinstalled.

That is what I meant by going into the Startup Options screen to manually select the new OS boot volume....changing the default Startup Disk System Setting is another way to achieve the same thing. I did stumble across your other thread where you posted a picture of the error message:

Is there an application that can be used … - Apple Community

These M-series Macs are very different than their older Intel models. Just about anything that goes wrong may result in this error message since macOS thinks there is an issue with the OS installation or perhaps even "Ownership" which I mentioned in another one of your threads on this forum. AFAIK, you can only use that bootable M-series USB drive on a single Mac due to "Ownership" issues.

Unfortunately it is nearly impossible to troubleshoot these boot issues due to the very restrictive nature of the M-series Macs and recent versions of macOS. Since you can boot to the original macOS on the internal SSD, you can try to access the macOS system logs from the new installation to see if they contain any clues, but in my personal experience they won't contain any useful information especially if this message appears very early in the boot process which I think it does.

Some things you can try:

• Check the health of the external drive using DriveDx (free trial period) and posting the complete text report here using the "Additional Text" icon which looks like a piece of paper. Maybe it will show a problem with the external drive. You will need to install a special USB driver in order to attempt accessing the external drive's health information.
• Run Disk Utility First Aid on the external drive....both the physical drive and the hidden Container. Within Disk Utility you may need to click "View" and select "Show All Devices" before the physical drives and hidden Containers appear on the left pane of Disk Utility. Even if First Aid says everything is "Ok", click "Show Details" and scroll back through the report to see if any unfixed errors are listed.
• Make sure to disconnect all other external devices from the Mac in case one of them is causing a problem.
• Connect the external drive directly to the Mac and try using a different USB-C cable.
• Did you completely erase the whole physical external drive? Many times external drives ship from the factory with odd partition layouts and even some data stored in areas that should not contain data. This can easily confuse a Mac, so it is best to erase the whole physical drive. You need to "Show All Devices" within Disk Utility as I mentioned earlier and erase the physical external drive as GUID partition and APFS (top option).
• Try a DFU firmware Revive which resets the security enclave chip & system firmware. Make sure to have a good backup of all data on the internal SSD because if this "Revive" process fails to complete you won't be able to access the data on the internal SSD.
• Clear the NVRAM by using the following command in the Terminal app (it is safe for both Intel & M-series Macs)....you will need to reboot afterwards making sure to access the Startup Options screen so you can manually choose the external drive as the startup disk. You want to avoid booting into your existing OS installations in case they modify the NVRAM before you can try booting the external drive. You may see a permissions issue related to being unable to change the computer name.

sudo  nvram  -c

Keep in mind, you will likely need to reinstall macOS no matter what when you try most of these steps since the OS on the external drive may no longer be salvageable depending on why the Mac thinks there is a problem.

While writing this response, I think the erasing of the external drive may be the critical factor here. Or the health of the drive (or issue with a cable or adapter).

What is the exact model of your external drive? Macs can be picky about the drives used for booting, so there is always a chance the external drive is just not compatible with booting an M1 Mac.

When you installed macOS to the external drive, were you prompted for choosing an admin user account for ownership of the OS for the external drive?

Just to confirm.....you currently have two bootable macOS volumes on the internal SSD? And you have the same issue installing macOS Ventura and Sonoma to the external drive?

Edit: Just thought of something else. What file system did you use when you erased the external drive? Was it APFS? And if it was, was it "Case Sensitive" or "Case Insensitive"? You want "Case Insensitive". If you used Case Sensitive, then that may be the problem.