Here is part of SVG code of the cyrcle with shadow created in Adobe Illustrator
<?xml version="1.0" encoding="utf-8"?>
<!-- Generator: Adobe Illustrator 24.1.2, SVG Export Plug-In . SVG Version: 6.00 Build 0) -->
<svg version="1.1" id="Layer_1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px"
viewBox="0 0 595.28 841.89" style="enable-background:new 0 0 595.28 841.89;" xml:space="preserve">
<style type="text/css">
.st0{fill:#FFF200;}
.st1{fill:none;stroke:#000000;stroke-miterlimit:10;}
</style>
<g>
<image style="overflow:visible;opacity:0.75;" width="1330" height="1384" xlink:href="data:image/png;base64,iVBORw0KG...
As you know vector graphics with shadow (or with any other style) effect created in Illustrator are raster effect. Here is the image preview from Illustrator. and it looks pixepixed

If you will use inIllustrator SVG filters that are located in 3d Effect and will apply SVG Shadow filter you will get this code
<?xml version="1.0" encoding="utf-8"?>
<!-- Generator: Adobe Illustrator 24.1.2, SVG Export Plug-In . SVG Version: 6.00 Build 0) -->
<svg version="1.1" id="Layer_1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px"
viewBox="0 0 595.28 841.89" style="enable-background:new 0 0 595.28 841.89;" xml:space="preserve">
<style type="text/css">
.st0{filter:url(#AI_Shadow_1);}
.st1{fill:#FFF200;}
.st2{fill:none;stroke:#000000;stroke-miterlimit:10;}
</style>
<filter filterUnits="objectBoundingBox" id="AI_Shadow_1">
<feGaussianBlur in="SourceAlpha" result="blur" stdDeviation="2"></feGaussianBlur>
<feOffset dx="4" dy="4" in="blur" result="offsetBlurredAlpha"></feOffset>
<feMerge>
<feMergeNode in="offsetBlurredAlpha"></feMergeNode>
<feMergeNode in="SourceGraphic"></feMergeNode>
</feMerge>
</filter>
<g class="st0">
<ellipse class="st1" cx="281.77" cy="381.06" rx="143.94" ry="150.51"/>
<ellipse class="st2" cx="281.77" cy="381.06" rx="143.94" ry="150.51"/>
</g>
</svg>
As you can see here the shadow used svg language for parsing shadow.
I think the reason is that Adobe XD do not use SVG filter when exporting SVG. But I am not shure...
