Ventura 13.4.1 external bootable drive refuses to start

FWIW called Apple Care and documented that after installing Ventura 13.4.1 (source the apple store),... was able to install a new OS to an external thunderbolt drive,... BUT upon selecting

"System_Settings>General>Startup_Disk"

from the newly installed OS (on and external drive),... and selecting the internal drive on my MacBookPro M1, what I get is an error message that says the OS has to be reinstalled,...

NOTE on my m1 also tried to,... Press and hold the power button until “Loading startup options” appears.

Change your Mac startup disk - Apple Support

BUT this method also failed,... so have to say IMHO that there is a problem that needs to be fixed by AppleSoftWare engineers

Case Number: 102040363400

No idea especially since I haven't tried installing macOS to an external drive on an Apple Silicon Mac yet. It is one of the things I will need to try in the very near future.

I do know that Macs are very picky about the drives used for booting, so that is always a possibility for the failure.

It also doesn't help that the Apple Silicon Macs have introduced a new concept of "ownership" which can also complicate things involving external boot drives especially when updating the OS on the external. I don't entirely understand this new "ownership" aspect, but just seen it mentioned a few times when someone tries to update a system with multiple boot drives.

Even on Intel Macs I have seen a Mac not reboot to the external drive to complete phase 2 of the installation. Many times I have had to manually select the external drive to boot so that the installation could complete. I don't know why some Macs are like this....seems to be independent of any specific version of macOS.

If you have rebooted and started phase 2 of the install process and it is interrupted, then you should be able to find the installer log stored on the external drive. I'm not sure where it would be located, but most likely either in "/Library/Logs" folder or "/private/var/log" folder (these paths are in relation to the root file system if the drive booted, not the mount point if accessing the drive from another boot drive which would likely add "/Volumes/<mount-point" to the path. If the install fails before starting to boot into Phase 2, then I don't know if the installer log is still saved there or not. It has been a while since I had to resort to looking for an installer log.

FWIW I'm an xPlane user (which is a FlightSim that can be FAA certified) that can run on multiple Macs networked together,...

https://www.x-plane.com/pro/certified/

https://x-plane.helpscoutdocs.com/article/34-using-networked-multiplayer-external-visuals-apps#:~:text=To%20set%20up%20a%20multi,over%20a%20Wi%2DFi%20network.

Anyway FWIW I run xPlane on a MacStudio and make a bootable duplicate of my internal SSD drive using SuperDuper (version 3.75)

https://www.shirt-pocket.com/SuperDuper/SuperDuperDescription.html

After upgrading to Ventura 13.4.1 I can no longer go to "System_Settings>General>Startup_Disk" and boot from a thunderbolt external drive from OWC (where-as before the latest Mac OS 13.4.1 I was able to boot from my thunderbolt external drive

https://eshop.macsales.com/shop/envoy-express/thunderbolt-3

The very legitimate reason I find it necessary to run from external thunderbolt drive(s) is because the flightSim is configured differently (and so I do testing of different aircraft configurations on the external drive and if things don't work, the way I have my various Macs setup which do the various computations for the flight sim physics model and the various external views,... if there is a problem (with a new configuration) I have a stable copy I can fall back up (on the internal SSD drives in my MacStudio/MacMini)

Doing some checking seems other people who upgraded to 13.4.1 also are encountering problems (booting from external drives)

https://apple.stackexchange.com/questions/461724/ventura-would-not-read-sandisk-ssd-after-update

https://forum.parallels.com/threads/boot-failure.360837/

hopefully APPLE software engineers fix this problem soon

It would be easier to make a clone of your drive using Carbon Copy Cloner then boot with that and make any updates after booting. I do that all the time to test as you want and no issue booting on my M1 or Intel mac.