Can't install macOS 15.4 on external volume

I have exactly the same issue. I own a M1 Mac mini and for almost three years I had a separate MacOS installation on an external thunderbolt nvme drive. Worked perfectly upgrading OS year after year. 15.4 comes, I am on 15.3.2 what could go wrong? . I go and update it, and suddenly get "The version of macOS on the selected disk needs to be reinstalled" . To further **** things down, for some reason my Time Machine backups don't work. I thought I'd have to upgrade OS on the integrated drive (big jump this time, from OS 12.x to 15.4) , and I managed to put it in 15.3.2, but I got the same message upgrading to 15.4 . I managed to install 15.4 on my internal storage using Apple Configurator - at the cost of erasing everything in there - though didnt have much in there. Once on 15.4 on the integrated storage I thought I could install 15.4 on my external drive (unrecoverable at this point) , and to my surprise, I still get the same error. Something is really messed up with 15.4 and Apple isn't acknowledging it.

Your suggestion to create another volume rather than partition has an extra advantage.

A partition is fixed in size which later on you might find to be either too big or too small whereas the extra volume is flexible and will stretch or shrink to accommodate what you put in or remove. (At least that was my understanding! 🫢)

Sequoia 15.4 tiene problemas para ser instalada desde 0.

Es la versión y el instalador de Sequoia lo que falla, no la forma en que formateas el disco.

Incluso en las MacBooks o equipos con M1 falla el instalador, dejando los equipos sin sistema, aparece exactamente el mismo mensaje que te aparece a ti de terminar la instalación.

Yo no puedo instalar MacOS desde el recovery o una USB booteable.

Solo queda esperar que se solucione por parte de Apple, no sé si en otra versión o en esta, lo que sí podrás hacer es instalar una versión inferior a Sequoia 15.4

If you can’t install macOS on an external disk

The implications from Apple are, it is possible

From a often referenced User Tip from @ Jack-19 Thanks for that 👍

Use an external SSD as your startup disk … - Apple Community

As for an earlier posting >> Unable to install macOS Sequoia update 15… - Apple Community

Unless I am missing something which is possible, on my 1 Double Expresso of the early day here

That posting was related to updating from earlier version of Sequoia to current 15.4 On To Internal Drive

So I am not sure how that relates to this

Yes, there have been several uses experiencing issues upDating to Sequoia 15.4

Yes, there were some issues downloading the Full Version of Sequoia 15.4 during the initial Release March 31 as !an R. Brown can testify to this

But Installing 15.4 to External Drives - not so much

Garry Brooke wrote:

UPDATE 2: Nope. Reformatted an entire SSD (GUID Partition Map) so that it had a single volume inside a single container. then tried to install macOS 15.4. As before, the install proceeds until "Closing applications and preparing to restart..." at which it hangs for some time then, it does a shutdown (I didn't see the usual "Startup in 30 seconds...." dialog). There is a startup bong then a very long delay (black screen at this point) then another bong and a quick startup from the internal SSD. Disk Utility shows there is an APFS System Volume and an APFS Data Volume.

So, I can't find any way of installing macOS 15.4 on an external drive. If anyone succeeds, please post here with details on how.

Sequoia 15.4 not installing on my externa… - Apple Community

For our collective reading purposes 😎

My version is 20.4.02 and has worked OK on both the internal SSD and the external.

I always keep a copy because you never know when you will need it again and it cuts out the hassle of downloading.

Regarding my previous comment, a couple of years ago I tried unsuccessfully to install the OS on my external several times and only discovered my mistake when I watched this short (4 minute) instructional video.

Using External As Boot Drive

I was making the classic mistake of accidentally formatting the Volume instead of the Disk.

The video takes you through every single step so you can't get it wrong.

Ian R. Brown wrote:

Your suggestion to create another volume rather than partition has an extra advantage.

A partition is fixed in size which later on you might find to be either too big or too small whereas the extra volume is flexible and will stretch or shrink to accommodate what you put in or remove. (At least that was my understanding! 🫢)

You are very correct

APFS Volumes over partitions which Lock things in

I’m curious, is this one of those “I want to” scenarios or is there a “need” to have Sequoia 15.4 on the external drive?

If we believe that the external drive with Sequoia 15.4 will be our backup plan in case the Mac Studio drive fails, then we should forget about this idea.

Apple Silicon computers absolutely need a functional internal drive. If the internal drive fails, which I haven’t seen happen yet, the external drive won’t work - no exceptions.

About installing Sequoia 15.4 on an external drive. Some people have been successful, like @Ian R. Brown, I think. But others have had trouble. 

Would suggest follow the previous advise from @ Ian R. Brown and use the Entire External Drive for the installation

There after, may be able to add a Volume

Partition a physical disk in Disk Utility on Mac

However, with APFS, you shouldn’t partition your disk in most cases.

Instead, create multiple APFS volumes within a single partition.

Make sure when you perform the install that the external drive is not connected to the USB-C port used for DFU Mode.....see the top section of the following Apple article:

Install macOS on an external storage device and use it as a startup disk - Apple Support

Also, when you went to install macOS onto the external volume, were you prompted to authenticate as a specific user/owner? If not, then that may be the problem.

It is also possible you may need to try a DFU Firmware Revive which resets the security enclave chip & system firmware and may help with "ownership" issues if the security enclave was having issues.

Well I and numerous others have had no difficulty.

Maybe the installer is defective?

Download a new one.

Did you watch the first couple of minutes detailing formatting in the video I posted?

Follow it step by step.

It may be boring but boring usually gets the job done.

Same. Update borked my external boot setup.

A great article on the case

https://eclecticlight.co/2023/03/15/ownership-of-apple-silicon-macs-matters-how-it-can-stop-external-bootable-disks/