Hello, Basically, my goal is to generate some simple graphics from Arduino input data using a Unity engine game. I'm having trouble even testing old games on this because my monitor is 1920x1080 and it seems impossible to change the output resolution, using Windows 10. When I change a game's resolution settings to lower it just doesn't work correctly and I would have to use windowed mode. Is there any way to output a fixed resolution and not care about the resolution it sees from the monitor?
You'll have to find your HDMI monitor's supported resolution (in its EDID profile.) A commecial HDMI monitor will support several. Windows' display driver reads that profile, then matches its GPU capabilities to show Windows Display's resolution choices. Your problems seesm to be that HDMI monitor is very restricted (e.g., can only support one or two resolutions) or its EDID information passing mechanism is defective. Finding the root cause of it is the first step.
I am using DxWnd to play older games which do not have proper solutions for APIs, hardware or resolutions https://sourceforge.net/projects/dxwnd/