Question:
<svg width='400' height='400' style='border: 1px solid black'>
<defs>
<clipPath id="myclipPath">
<polygon points="20,30 40,10 60,30" fill='red'/>
</clipPath>
</defs>
<circle clip-path="url(#myclipPath)" r="100" cx="50%" cy="50%" fill="green"/>
</svg>
Answer:
Clipping doesn't cut anything because outside the circle :
As well as here: https://codepen.io/topicstarter/pen/KKpgLYZ I drew around the girl along the contour of her body and the clip-path worked and by the way outlined my hands, that is, manual work
To cut it out, you need to put a polygon more accurately and draw it on a circle
<svg width='400' height='400' style='border: 1px solid black'>
<defs>
<clipPath id="myclipPath">
<polygon points="20,30 40,10 60,30" fill='red'/>
</clipPath>
</defs>
<circle r="100" cx="50%" cy="50%" fill="green"/>
<polygon points="20,30 40,10 60,30" fill='red'/>
</svg>
In this example, the clipping is cutting, changing only the coordinates of the circle
<svg width='400' height='400' style='border: 1px solid black'>
<defs>
<clipPath id="myclipPath">
<polygon points="20,30 40,10 60,30" />
</clipPath>
</defs>
<circle r="100" cx="0%" cy="0%" fill="green" clip-path="url(#myclipPath)"/>
</svg>