Normally, for UEFI boot, you could be able just to create a FAT32 partition and copy the ISO content there. In the past, it was perfectly workable way to do so.
Except for the unfortunate install.wim file. The first releases of Windows 10 were fine, they had it under 4GB, but some of the half-year releases have it grown over 4GB, and FAT32 cannot handle that. Thus all the mitigations you see here.
The Microsoft's USB tool does not use install.wim; it contains install.esd instead. It is basically the same thing, but with different compression, so it is still a bit under 4GB. You can recompress install.wim into install.esd, if you have the inclination ...and a windows machine nearby (dism /export-image).
Except for the unfortunate install.wim file. The first releases of Windows 10 were fine, they had it under 4GB, but some of the half-year releases have it grown over 4GB, and FAT32 cannot handle that. Thus all the mitigations you see here.
The Microsoft's USB tool does not use install.wim; it contains install.esd instead. It is basically the same thing, but with different compression, so it is still a bit under 4GB. You can recompress install.wim into install.esd, if you have the inclination ...and a windows machine nearby (dism /export-image).