From a 32bit process, Win32::IsDeveloperModeEnabled() can't see the 64bit registry key where the developer mode setting is stored. It's using a wrong (similarly named) constant to set the dwFlags argument

KEY_WOW64_64KEY is a "Registry Access Right" constant defined in winnt.h as 0x0100 - https://docs.microsoft.com/en-us/windows/win32/sysinfo/registry-key-security-and-access-rights

The correct constant to use is RRF_SUBKEY_WOW6464KEY which is defined in winreg.h as
0x00010000 - https://docs.microsoft.com/en-us/windows/win32/api/winreg/nf-winreg-reggetvaluea#RRF_SUBKEY_WOW6464KEY

Note: The RRF_SUBKEY_WOW6464KEY constant is only defined in the Windows 10 SDK, and I'm building Perl with the 8.1 SDK, and then running that binary on Windows 10 machines.