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#11
Just wanted to give a quick update about this - which I have now solved.
It turns out that the SSD was stuck in hibernate, which made it impossible to access and fix. I realized this by booting in a USB-based version of Ubuntu: the SSD was visible, but not accessible.
I then used the Dell BIOS to wipe the disk, and was able to then use the Media Creation Tool USB installer to:
(1) go to command prompt and reformat the disk using Diskpart
(2) install Windows 10 on the formatted SSD
It now works perfectly well. I'm still unsure how exactly the disk ended up being stuck in that mode though!
Thanks for the help!