I know HTML's filter: blur(5px) can blur the entire image with a blur radius of 5px. What if I want to blur only a specific part of an image? Like a blur pen, which works only on a specific area of an image. How can I do that?

I have layers of svg as shown in the screenshot below

For example, if you see the image below, specific parts of an image are blurred. How can I do that?