GoKawiilGuide details Wi-Fi and HDMI methods to turn a spare laptop into second monitor
The guide outlines how to repurpose a spare laptop as a second display: Mac-to-Mac users can use AirPlay on MacBooks from 2018 or later by enabling AirPlay Receiver in System Settings and linking both devices via the same Apple ID. For mixed operating systems, including Windows and Linux machines, it recommends Deskreen, a free open-source tool that connects laptops over shared Wi-Fi via a QR code or URL, with an HDMI dummy plug needed to extend rather than just mirror the display.