Using a mac as a mirror screen for a pc
How can I use my Mac as a screen mirror for my windows10 laptop
Old laptop with only USB3.0a and HDMI ports
Thanks
iMac 21.5″, macOS 10.15
Use of any Mac as a true external monitor for a non-Apple device was never supported, intended or documented.
When COVID hit, some grossly under-informed web journalists lacking any basic research skills or moral compasses wrote articles suggesting any iMac could be used as a monitor for any other device. It's internet bunk.
A standard external monitor is cheaper, easier to connect, allows a true extended desktop, and uses less energy than an imac.