Why does my MinGW-w64 generates 32-bit binaries? They can't run if their stack size is more than ~2GB, compatibility mode is on Windows XP by default, and -m64 option doesn't works (64-bit mode is not compiled in.).
Which exact file did you download? The installer, mingw-w64-install.exe? If so, it lets you choose if you want an x32 or x64 compiler. Consider using a different MinGW distribution (the one you used has an outdated GCC). The two good ones are msys2.org and winlibs.com – HolyBlackCat