You cannot legally download and install macOS for free on a non-Apple device. macOS is exclusively designed and developed by Apple Inc. for its own hardware, and the operating system is only available for installation on Apple Macs or through virtual machines running on Apple hardware.

While some users have managed to install macOS on non-Apple hardware using custom bootloader software, such as Hackintosh, this is a violation of Apple's software license agreement and is considered piracy. Installing macOS on non-Apple hardware can also lead to compatibility issues and instability, as the software is not optimized for hardware configurations other than those designed by Apple.

In terms of installing macOS as a dual OS alongside Windows, it is possible to do so on an Apple Mac using the built-in Boot Camp utility. Boot Camp allows you to partition your Mac's hard drive and install Windows alongside macOS, enabling you to switch between the two operating systems at startup.

However, if you want to install macOS on a non-Apple device alongside Windows, you will need to create a Hackintosh system, which, as mentioned, is not a legal or reliable option. Additionally, even if you are able to install macOS and Windows as dual OS on a non-Apple device, you may encounter compatibility issues and instability, as the software is not designed or optimized for the hardware configuration of your device.

In summary, it is not legal or advisable to download and install macOS on a non-Apple device for free. If you want to use macOS, you will need to purchase an Apple Mac, or alternatively, use a virtual machine to run macOS on an existing Apple device. While it is possible to install macOS as a dual OS alongside Windows on an Apple Mac using Boot Camp, this is not a viable option for non-Apple devices.