installing windows on mac on a new hard drive

I am not sure 'why'? I guess because Parallels works through Apple's Bootcamp Assistant when in macOS, to find and connect to a Windows Partition, and since Bootcamp Assistance does not support non-primary SSD installs, so Parallels does not 'see' these. But, Parallels does not support Bootcamp Windows installs that are not on the primary SSD - and I've just had an amusingly circular conversation with their tech support to confirm this. However, I'd like to be able to 'run-Windows within Parallels' through Bootcamp, without Windows being on my primary drive. TB3 is a faster interface than SATA so this is the better arrangement for a separate OS. ie the macOS/Bootcamp environment has no issue with detecting and running either OS. I can also 'restart into' from both OSes. This works perfectly - it's detected from power-on, I get the macOS or Windows10 drive-choices to boot into. I've a separate SATA SSD now on that channel for storage, and I have hacked my way using VMFusionWare to a Windows 10 bootcamp install on a TB3-connected NMVe SSD in an external enclosure. I hated the Fusion drive so replaced the m'board blade SSD with one large enough to replace the whole virtual drive array of the Fusion Drive. We all know that 128 gb is not enought these so we might have bought something like a an external HDD for some additional storage.I recently replaced my CPU, RAM and Fusion-Drive in my 19,1 iMac - awesome upgrade. If you have bought something like a baseline MacBook pro and saved a little cash, but then soon hit with the storage issue when trying to install windows using Bootcamp

Installing windows on mac on a new hard drive