Just so you know, I don't use Windows Defender as my AV, I use Avast One (the registered version, not the free version), so I'm not exactly sure if it has an exclusions list (but I assume that like most AV programs that it does). So... The only other thing that I can think of that might help, is to add the installer(s) to Windows Defender's exclusion list before installing. Hopefully doing that will prevent you from getting the message you see when installing it.

Note. I have also added the location of my Captain Sim product installers, AND the folders that my flight sims (FSX, FSX-SE, P3Dv3, P3Dv4, and P3Dv5) are installed, to the Exclusions list, and I have never seen any messages about them failing to be installed, nor have I had any issues where my AV has found any of Captain Sim's files as a threat (false positive), and so they work fine. I haven't had any problems with viruses in many years since I first started using Avast Free, followed by Avast One Free, and then the registered version of Avast One.