Rufus worked like a charm for me as well. My steps, which I followed on a separate Windows machine:
- Download Rufus.
- Download Windows 10 ISO (I downloaded and ran the Windows media creation tool and selected the local ISO option).
- Plug in the expansion card (on the separate machine, not my framework laptop).
- Run Rufus. Select “List USB Hard Drives” under “advanced drive properties” to make the storage card visible. Select the ISO, select the “windows to go” preset, and click “start”.
And that was it! After Rufus was done, I unplugged my storage card from the other machine and put it back in my framework laptop. I turned it on, spammed f12, selected the storage card as my boot media, and voila: I was in Windows.