import FORM_FACTOR from ‘@salesforce/client/formFactor’ can be used to find the viewing device in Salesforce Lightning Web Component using which we can Hide and Show based on the viewing Device.

Sample Lightning Web Component:

HTML:

<template>
    <lightning-card>
        <div class="slds-p-around_medium">
            <template if:true={desktopBool}>
                Desktop Device
            </template>
            <template if:true={iPadBool}>
                iPad Device
            </template>
            <template if:true={iPhoneBool}>
                iPhone Device
            </template>
        </div>
    </lightning-card>
</template>

JavaScript:

import { LightningElement } from 'lwc';
import FORM_FACTOR from '@salesforce/client/formFactor';

export default class SampleLightningWebComponent extends LightningElement {

    iPhoneBool = FORM_FACTOR == 'Small' ? true : false;
    iPadBool = FORM_FACTOR == 'Medium' ? true : false;
    desktopBool = FORM_FACTOR == 'Large' ? true : false;

}

js-meta.xml:

<?xml version="1.0" encoding="UTF-8"?>
<LightningComponentBundle xmlns="http://soap.sforce.com/2006/04/metadata">
    <apiVersion>60.0</apiVersion>
    <isExposed>true</isExposed>
    <targets>
        <target>lightning__Tab</target>
    </targets>
</LightningComponentBundle>

Output: