I think the reason it’s not woking for you is because you’re using USB external cases. The method I posted was for ‘internal’ PCIe SSD boards.
Have a look here:
NOTE: Since my post, the CURL method of install is no longer supported by Umbrel. You will have to flash the Umbrel OS directly to the NVMe SSD (using one of those USB enclosures you have) and then run the install from there once the instructions for preparing the PiOS are done.