I'm new to CNC having built a 2-axis plotter driven by Arduino, CNC-Shield and GRBL 1.1.

I can draw a square.

I now want to draw a circle and have failed miserably for days.

I have googled on and off for about a week now and looked at dozens of examples. Not one of them does a circle. Not on my machine nor in any of about 5 different simulators I've tried. At best a limp arc, at worst straight lines or nothing.

Come on.

A circle.

Could someone post the GCode to do say a circle centered at X=0,Y=0 with radius 5cm?

Since I now believe it is impossible. Please check your work here:
GCode Simulator
or here:
https://nraynaud.github.io/webgcode/