I'm not sure if I fully understand your issue, but if you have a Mac and a Windows PC:
- if the PC came with Windows the license is probably tied to that machine (the manufacturers pay less for a copy of Windows than we do, but that copy is limited in the sense that it will work only on that machine);
- if you have purchased a copy of Windows 10 Home and you installed it on a PC, and now you want to use Windows on your Mac via Bootcamp, you can transfer the license to the new installation and remove the activation from the previous PC;
- if you have a Windows 10 PC which you want to continue running and you want to add another installation of Windows in Bootcamp, you will need to purchase a new copy of Windows;
- once you have a dual booting Mac with macOS on one side and Windows on the other side, you can use VMWare Fusion to run your Windows partition as a virtual machine (I haven't ever done it so I can't be more informative about this).
One license = one installation. You can transfer it between if you purchased it on your own, you generally can't if Windows came preinstalled in a PC you bought.
I don't know about inactivated copies of Windows. Sure, they do run, but I don't know which are the limitations.
For further information in this article you have a pretty comprehensive explanation of the various scenarios:
https://www.howtogeek.com/261053/when-can-you-move-a-windows-license-to-a-new-pc/.