First, this is dangerous (for your data only) what are you doing over there, please suppose/rethink what would happen by hitting Enter keycap when your /home (data collection) directory indeed lives inside your secondary SATA/USB SSD or of=/dev/sdb, as you have put this within command of “your” (but not only) choice. Therefore please use sudo fdisk -l before (every time, always) you start to copy/paste commands from some Internet site into your Terminal. And, fdisk -l would show you that your SD Card is mounted on /dev/mmcblk[x]p? (usually), and not as /dev/sd[x]?.
Second “thing”, “if=/path/to/” doesn’t exit! This just means you need to cd to that particular /home folder (path) where downloaded amd64.hybrid.iso (doesn’t matter which one) resides. And (to your advantage), that you were in wrong path/directory when executing if=/path/to/pureos-9.0-gnome-live_20200806-amd64.hybrid.iso saved your /dev/sdb data at the first place (needs to be understood well).
Where “the image” name is PureOS, which doesn’t support X64 UEFI indeed (not at this moment), but upcoming pureos-10-gnome-live (without devel) might be tailored up to your request here.
But not UEFI (meaning UEFI isn’t or wasn’t disabled). If P14s Gen 1 (slight chance for Legacy Boot), please disable Secure boot and enable (switch to) what necessary, as @spacemanspiffy recommended already. Also, you should preferably put .iso on USB stick only (of=/dev/sdX), as @tracy recommended already. Also, if this (or any other) support.lenovo.com recommendation doesn’t work for you, by recognizing that you need to bring everything back as it was within your BIOS, as otherwise you wont be able to (re)start your Windows 10 installation. Therefore please rethink carefully your steps or just leave PureOS Live aside, especially aside until you understand well what Legacy Boot means (as prerequisite for this Live image you want to load on your HW). Just don’t rush into copy/paste Terminal commands without knowing exactly what they mean, 
(as even Ubuntu community won’t be able to help you after your data is gone).
Please read through this thread as well:
P.S. @BrunoG, don’t get me wrong, please, as otherwise I just wasted my time, and this wasn’t my intention at all.