We can make use of SLDS Modal CSS and avoid the popup if we avoid the slds-container CSS class.

Please check the following sample Lightning Web Component for reference.

Sample Lightning Web Component:

HTML:

<template>
    <div class="modal-header slds-modal__header">
        <h4 class="title slds-text-heading--large">Title</h4>
    </div>
    <div class="slds-modal__content slds-p-around--x-large">
        Sample Content
    </div>
    <div class="slds-modal__footer">
        <div class="slds-align_absolute-center">
            Footer
        </div>
    </div>
</template>

JavaScript:

import { LightningElement } from 'lwc';

export default class SampleLightningWebComponent extends LightningElement {
}

js-meta.xml:

<?xml version="1.0" encoding="UTF-8"?>
<LightningComponentBundle xmlns="http://soap.sforce.com/2006/04/metadata">
    <apiVersion>62.0</apiVersion>
    <isExposed>true</isExposed>
    <targets>
        <target>lightning__Tab</target>
    </targets>
</LightningComponentBundle>

Output: