To apply an SVG filter to straight lines, set filterUnits="userSpaceOnUse", otherwise the straight lines/ paths are not shown.
Built with blockbuilder.org
xxxxxxxxxx
<head>
<meta charset="utf-8">
<style>
path {
stroke: blue;
stroke-width: 5px;
fill: black;
}
</style>
</head>
<body>
<svg width="300" height="300">
<filter id="blurMe" filterUnits="userSpaceOnUse">
<feGaussianBlur in="SourceGraphic" stdDeviation="5" />
</filter>
<path d= "M 100 100 L 200 100" filter="url(#blurMe)"/>
<path d= "M 200 100 L 200 200" filter="url(#blurMe)"/>
<path d= "M 200 200 L 100 200" filter="url(#blurMe)"/>
<path d= "M 100 200 L 100 100" filter="url(#blurMe)"/>
<path d= "M 100 100 L 200 200" filter="url(#blurMe)"/>
<path d= "M 200 100 L 100 200" filter="url(#blurMe)"/>
</svg>
</body>
</html>