In light of your third "Conclusions" and your #2 conclusion being contrary to other reports, do you suspect a problem with your Samsung SSD?
It had occurred to me the Thunderbolt 3 standard is very broad and as a result there have been some very different performance and other variations, particularly in the PC realm. (We haven't seen that nearly as much in Macs as Apple has always rigorously adhered to the maximums permitted in the standard.) I would be tempted to speculate Samsung used a more minimal approach to the standards if it weren't for the fact that I attempted to create a bootable volume on an OWC Aura Thunderbolt 3 SSD that exhibits a performance curve very close to the internal SSD in the previous Intel Mac mini and if anything the Samsung install got further along than the OWC install.
Using the flash drive installer should have eliminated any software variations but I did NOT connect directly to a Thunderbolt 4 port and instead used either a daisy chained or distributed connection which potentially might have made a difference. At that point the number of possible permutations starts to expand dramatically and I am not inclined to spend the time and energy it would take to explore all of the possibilities. I have succeeded in meeting my objective of reliably creating a bootable external drive for my M1 Mac mini and I am confident in my conclusion "...it is not difficult to create a bootable external drive for M1 macs given the right combination of connecting media, drive media, and installer
", or perhaps I should have been more emphatic in expressing my caveat. 🤷♂️
I wonder if Apple's difficulty getting their ASR¹ utility to work on the M1 Macs might be related to the difficulty so many users are encountering creating bootable external drives? My success using the slower USB 3.x devices has also led me to speculate the speed with which the M1 SoC moves data internally might be creating timing errors that are contributing to the problem, but that seems unlikely.
¹Apple Software Restore — the BSD utility used by Carbon Copy Cloner© to create bootable macOS 11 clones.