I'm using Windows 10.
Well, I have unique installs that are themed, and to keep the install size manageable, with aircraft & scenery pertinant to each install, & it prevents any scenery conflicts that could occur. I also have unique splash screens & gui per install.
So, I have the following installs: Golden Wings, Ford Tri-Motor Project, Alaska, Vintage (pre WWI), History (WWI era), Heritage (WWII era), Space (Carl Reddin's Space scenery, with Lost in Space scenery & a whole bunch of spacecraft), Then I have a FS2004SE install with aircraft & scenery that our local VA club uses & I also have a test install as well.
& I have a clean install on a portable drive that I just copy, paste & rename should I need extra installs, or if anything bombs out.
Over the years, I must have used that for over 40 installs on various PC's
So, they all work perfectly in Windows 10.. No issues.