Hi,

Use the following code to block the UI and show the loading spinner:

import { Component } from "@odoo/owl";
// here you can import the use service hook
import { useService } from "@web/core/utils/hooks";


export class Spinner extends Component {
    static template = "SpinnerTemplate";
    setup() {
        // In odoo already has more services we can  use the ui-service from useService hook
        this.uiService = useService("ui");
    }

    showSpinner() {
        // When the function is called, the user interface will be blocked
        // and a loading spinner will be displayed.
        this.uiService.block()
    }

}
<t t-name="SpinnerTemplate">
    <h1>Block Ui</h1>
    <!--the button to trigger the function showSpinner-->
    <button t-on-click="showSpinner">Show Spinner</button>
</t>

Hope this helps.