As far as I know, there is no such ootb web part to display the layout. You need to display react-script-editor in SharePoint Online. Then you can add custom js and css file to the modern page.
<div class="row">
<div class="col-4">
<nav id="navbar-example3" class="h-100 flex-column align-items-stretch pe-4 border-end">
<nav class="nav nav-pills flex-column">
<a class="nav-link" href="#item-1">Item 1</a>
<nav class="nav nav-pills flex-column">
<a class="nav-link ms-3 my-1" href="#item-1-1">Item 1-1</a>
<a class="nav-link ms-3 my-1" href="#item-1-2">Item 1-2</a>
</nav>
<a class="nav-link" href="#item-2">Item 2</a>
<a class="nav-link" href="#item-3">Item 3</a>
<nav class="nav nav-pills flex-column">
<a class="nav-link ms-3 my-1" href="#item-3-1">Item 3-1</a>
<a class="nav-link ms-3 my-1" href="#item-3-2">Item 3-2</a>
</nav>
</nav>
</nav>
</div>
<div class="col-8">
<div data-bs-spy="scroll" data-bs-target="#navbar-example3" data-bs-smooth-scroll="true" class="scrollspy-example-2" tabindex="0">
<div id="item-1">
<h4>Item 1</h4>
<p>...</p>
</div>
<div id="item-1-1">
<h5>Item 1-1</h5>
<p>...</p>
</div>
<div id="item-1-2">
<h5>Item 1-2</h5>
<p>...</p>
</div>
<div id="item-2">
<h4>Item 2</h4>
<p>...</p>
</div>
<div id="item-3">
<h4>Item 3</h4>
<p>...</p>
</div>
<div id="item-3-1">
<h5>Item 3-1</h5>
<p>...</p>
</div>
<div id="item-3-2">
<h5>Item 3-2</h5>
<p>...</p>
</div>
</div>
</div>
</div>
For more samples you can refer to following document
https://getbootstrap.com/docs/5.3/components/scrollspy/
For deployment of spfx you can refer to following document
https://learn.microsoft.com/en-us/sharepoint/dev/spfx/sharepoint-framework-overview
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