Compared to older Mingw64 environments those link with the latest UCRT so you get almost the same style executable as Visual Studio.
The only difference for C is that it uses Mingw exception handling and global initialization code, and it uses Itanium ABI for C++.
A major part of the incompatibility with older versions of Windows is just because newer VS runtimes cut the support artifically. That's it. Many programs would otherwise work as-is or with just a little help.