Filter Bar can be set up with a vertical or a horizontal layout. When using the horizontal layout, you can choose the default state: “collapsed until opened” or “show already on page load.”

Layout and default state settings for Filter Bar under Events > Settings > Filters

On a smaller screen, however, to save screen space for the content, Filter Bar is hidden by default. There is no built-in setting to change this.

In case you would like to have Filter Bar open by default on mobile as well, then the following snippet will do the trick.

<?php
/**
 * Open the Filter Bar on mobile on initial pageload.
 *
 * By default, Filter Bar is closed on mobile regardless of the setting.
 * With this snippet Filter Bar will show on pageload when using the horizontal setup.
 *
 * Usage: Add the snippet to your functions.php file or with a plugin like Code Snippets.
 *
 * @author: Andras Guseo
 *
 * Plugins required: The Events Calendar, Filter Bar
 * Created: January 19, 2024
 */
function tec_open_filterbar() {
	echo '<script>
	let fbSelector = document.querySelector(".tribe-filter-bar.tribe-filter-bar--horizontal");
	if(fbSelector != null) {
		fbSelector.classList += " tribe-filter-bar--open";
		fbSelector.style.position = "unset";
	}
	</script>';
}

add_action( 'wp_footer', 'tec_open_filterbar' );

Source: https://gist.github.com/andrasguseo/a22cbb1917c98a9fbf5a47c012b37d76

Copy-paste this code into your child theme’s functions.php file, or better, use a plugin like Code Snippets.

(You can read more about this topic in our Using Custom Code Snippets article.)