createCanvas(400, 400, WEBGL);

  let b = createFramebuffer()

  background(0);

  b.begin()

    fill(255,0,0)

    noStroke()

    rect(-100,-100,200,200)

​

    erase()       // This is Erasing the Main Canvas, rather than the framebuffer

    circle(0,0,100)

    noErase()

  b.end()

  image(b,-200,-200)

}