To find Guest User Context in Salesforce Lightning Web Component, import @salesforce/user/isGuest property.

Sample Lightning Web Component:

HTML:

<template>
    <lightning-card>     
        <div class="slds-var-p-around_medium">
            <lightning-input 
                type="checkbox" 
                label="Guest User"
                checked={isGuestUser}
                disabled>            
            </lightning-input>
        </div>   
    </lightning-card>
</template>

JavaScript:

import { LightningElement } from 'lwc';
import isGuestBoolean from "@salesforce/user/isGuest";

export default class ExperienceCloudComponent extends LightningElement {

    isGuestUser = isGuestBoolean;

}

js-meta.xml:

<?xml version="1.0" encoding="UTF-8"?>
<LightningComponentBundle xmlns="http://soap.sforce.com/2006/04/metadata">
    <apiVersion>58.0</apiVersion>
    <isExposed>true</isExposed>
    <targets>
        <target>lightningCommunity__Page </target>
    </targets>
</LightningComponentBundle>

Output: