I rode for years and years without ever learning to idle, then I saw someone doing it, and got a few ideas off them, and learned fairly quickly thereafter.
First: get the tyre pumped up good and hard, as squidgy tyres put an extra ‘variable’ into the equation.
Second, for similar reasons, choose a good smooth level piece of ground.
Consider lowering the seat a tad. (A tad = 10 gnat’s eyebrows and is sometimes called a decagnat. Likewise, a gnat’s eyebrow is occasionally called a decitad.)
Now, riding fairly slowly forward, do what you have called a ‘stall’, which I interpret as a fairly sudden stop, with one pedal down.
In the stall, the wheel will run slightly ahead of your centre of gravity. The momentum of the wheel will push your foot up a little behind you.
Now, push that foot down again in a smooth movement.
Keep looking ahead as you do this.
The uni should pass under your centre of gravity and your foot will be pushed up slightly in front of you.
Now ride off.
Repeat this sequence: stall, back, ride off. Stall, back, ride off.
Move onto: stall, back, forward, back, ride off.
Aim for a positive pendulum movement. You are moving between two positions: leaning too far backwards and leaning too far forwards. You should not try to be perfectly balanced at all parts of the movement.
Incidentally, the wheel track should be a series of N shapes, not H shapes. (H shapes would be a challenge. ;0) )
I found that learning idling and learning to ride backwards were closely linked. When you have the confidence and ability to back pedal a complete revolution rather than about 1/3 of a revolution, you have made a break through.
I did NOT find it helpful to try idling whilst leanin against a wall, or holding a post. You might.
Once you can do about 7 pedal strokes, get into the habit of counting pedal strokes and keeping a ‘best score’. Once you can regularly do 10 pedal strokes, you’re well on the ay to being able to idle indefinitely.
And don’t look at the ground.
Good luck. :0)