There is still some Windows XP and higher - checking in the OpenJDk coding, see

https://github.com/openjdk/jdk/blob/70e786154fae78c0dacaa3e29c7aa4d3d14b892b/src/jdk.accessibility/windows/native/jabswitch/jabswitch.cpp#L56
https://github.com/openjdk/jdk/blob/70e786154fae78c0dacaa3e29c7aa4d3d14b892b/src/java.desktop/windows/classes/sun/awt/windows/WPathGraphics.java#L315

We compile currently with Windows 8+ settings :

# _WIN32_WINNT=0x0602 means access APIs for Windows 8 and above. See
# https://docs.microsoft.com/en-us/cpp/porting/modifying-winver-and-win32-winnt?view=msvc-170
ALWAYS_DEFINES="-DWIN32_LEAN_AND_MEAN -D_WIN32_WINNT=0x0602 \

So everything handling older versions than Windows 8 could most likely be removed.