Hi,
I have created a drop down menu in lightning web component. But, I want a pop up will appear on click of a menu item. 
I tried this for pop up, But it is not working. On click of a "Rename " Menu item . A pop up will be shown.

button.html

<template>
    <div class="slds-p-around_medium lgc-bg">
        {selectedItemValue}
        {ready}
        <lightning-card title="Drop Down">
            <lightning-button-menu alternative-text="Show menu" variant="border-filled" onselect={handleOnselect}>
                {selectedItemValue}
                <lightning-menu-item value="openinsharepoint" label="Open in SharePoint" prefix-icon-name="utility:new_window"
                    href="#"
                    target="_blank">
                </lightning-menu-item>
                <lightning-menu-item value="rename" label="Rename" prefix-icon-name="utility:edit">
                    <template if:true={ready}>
                        <section role="dialog" tabindex="-1" class="slds-modal slds-fade-in-open slds-modal_small"
                            aria-labelledby="modal-heading-01" aria-modal="true" aria-hidden="true"
                            aria-describedby="modal-content-id-1">
                            <div class="slds-modal__container">
                                <!-- Modal/Popup Box LWC header here -->
                                <header class="slds-modal__header">
                                    <button class="slds-button slds-button_icon slds-modal__close slds-button_icon-inverse" title="Close" onclick={closeModal}>
                                        <lightning-icon icon-name="utility:close"
                                            alternative-text="close"
                                            variant="inverse"
                                            size="small" ></lightning-icon>
                                        <span class="slds-assistive-text">Close</span>
                                    </button>
                                    <h2 id="modal-heading-01" class="slds-text-heading_medium slds-hyphenate">Rename LWC Setup.docx</h2>
                                </header>
                                <!-- Modal/Popup Box LWC body starts here -->
                                <div class="slds-modal__content slds-p-around_medium" id="modal-content-id-1">
                                    <lightning-input type="text" name="folder_name" label="Rename" placeholder="Enter new item name">
                                    </lightning-input>
                                </div>
                                <!-- Modal/Popup Box LWC footer starts here -->
                                <footer class="slds-modal__footer">
                                    <button class="slds-button slds-button_neutral" onclick={closeModal} title="Cancel">Cancel</button>
                                    <button class="slds-button slds-button_brand" onclick={submitDetails} title="Create">Create</button>
                                </footer>
                            </div>
                        </section>
                        <div class="slds-backdrop slds-backdrop_open"></div>
                    </template>
                </lightning-menu-item>
                <lightning-menu-item value="download" label="Download" prefix-icon-name="utility:download">
                </lightning-menu-item>
                <div class="slds-has-divider_top-space" role="separator">
                    <lightning-menu-item value="delete" label="Delet" prefix-icon-name="utility:close"></lightning-menu-item>
                </div>
            </lightning-button-menu>
        </lightning-card>
    </div>
</template>

button.js

import { LightningElement, track } from 'lwc';
export default class ButtonMenuOnselect extends LightningElement {
    @track selectedItemValue;
    @track ready;
    handleOnselect(event) {
        this.selectedItemValue = event.detail.value;
        if(this.selectedItemValue == "rename")
        {
        alert("ready");
        this.ready = true;
        alert("false");
        }
        
    }
}