Extend PC desktop to iMac

There are so many conflicting ways about extending a windows desktop to iMac...ie using iMac as an external monitor for windows. Some say you can do it...some say you cant do it....some say depending on the iMac.....

Now i do know that both machines that i have can use target display mode when both machines are booted into Mac OS.....i have done it and it works...so i know how to do that........

My question is this:

I would like to use the iMac as an external monitor for Windows that is on the Mac book Pro either using a thunderbolt cable (preferred) as both machine have thunderbolt ports....or any other way, without additional software.

Can this be done ?

• • I am Running an iMac 21.5 inch, Late 2013 model with Catalina Ver 10.15.2
  • I am running a Mac book Pro Model 11,4 (think it is a mid 2015 model) using Boot Camp with Windows 10 home.
  • Both Machines do have windows installed via boot camp...but my question is based around using the iMac as an external monitor while booted into Mac OS...
    • If not possible....how to do it if both machines were booted into Windows via boot camp using either an Ethernet cable or thunderbolt cable...without additional software