Its a heck of a lot easier to run macOS on an external drive then windows. MS supported this Windows to Go but that's only available with the enterprise version of windows and updating windows to go is problematic (at least it was for me).
Recently, MS ended development of Windows to Go, either they have something else up their sleeve or official support for windows on external drives is ending - I have no idea what's up.
For me, I found it far easier to install windows on my iMac's internal storage and then boot the iMac off an external SSD when I needed macOS. Maybe its easier now, as I've not researched it but back then getting windows on an external drive was involved at best. The link I pasted above seemed to indicate that it may not be a hassle but I have no idea, as I've not tried it.