Looking for Virtual Monitor software for Mac

Decades ago when large monitors were expensive, there was software that allowed me to have a virtual second monitor. You could set the size of the virtual monitor to just about ANYTHING you'd like; you were not limited by the size of your current connected monitor.

I'm trying to find something like that now. I want either a huge virtual monitor or software that allows me to extend out my current monitor beyond the maximum 3840 x 2160 setting. When my mouse gets to the edge of the monitor, the background scrolls until I hit the virtual monitor's size.

By the way, I'm not talking about Spaces nor Mission Control nor the Zoom feature in Accessibility.

Anyone know of software out there that can expand a monitor or virtual monitor beyond a default monitor size?