Will booting Surface Book 2 from USB flash drive erase the windows product key in the firmware?

Solution 1:

No, reinstalling Windows (or any other operating system) will not erase the embedded product key. Only a defective UEFI firmware update could do that.

Additionally, Windows restores its activation automatically from Microsoft servers, if the hardware remains (largely) unchanged—even without an embedded product key.

So just go ahead and do a clean reinstall, it’s the correct choice!