This MU-Plugin helps change "out of stock" text to what you want either on single product page or loop page, or both. make sure you edit the $out_of_stock_span_class to your use case. Use at your risk, enjoy! I mean, what's life without taking risks? 🚀 Inspired by: https://woocommercecommunity.slack.com/archives/CV9AF72PR/p1651253141682729

pekky-wc-change-out-of-stock-text.php

<?php
/**
 * WooCommerce Change "out of stock" text.
 *
 * @package pekky-wc-change-out-of-stock-text
 * @author Precious Omonzejele (CodeXplorer 🤾🏽‍♂️🥞🦜🤡)
 *
 * @wordpress-plugin
 * Plugin Name: WooCommerce Change "out of stock" text
 * Plugin URI: https://gist.github.com/Preciousomonze/c0d49effe8e3d613f838aa35f352bfc9
 * Description: This MU-Plugin helps change "out of stock" text to what you want either on single product page or loop page, or both. make sure you edit the $out_of_stock_span_class to your use case.
 * Author: Precious Omonzejele (CodeXplorer 🤾🏽‍♂️🥞🦜🤡)
 * Author URI: https://codexplorer.ninja
 * Version: 1.0.0
 * Requires at least: 5.0
 * Tested up to: 5.9
 * WC requires at least: 5.0
 * WC tested up to: 6.0
 */

class Pekky_WC_Change_Out_Of_Stock_Text {

	/**
	 * Alt Text to replace it with.
	 *
	 * Note: change this in init function, so it can support translation.
	 * 
	 * @var string
	 */
	public static $alt_text = '';

	/**
	 * Your out of stock parent class on loop page.
	 *
	 * Should be the closest parent element.
	 * 
	 * @var string
	 */
	public static $out_of_stock_parent_class = 'product';

	/**
	 * Your out of stock span class on loop page.
	 *
	 * This can be different depending on your theme.
	 * Mostly used for the shop/loop page.
	 *
	 * @var string
	 */
	public static $out_of_stock_span_class = 'out-of-stock';

	/**
	 * Enable for Single Page.
	 *
	 * @var bool
	 */
	public static $enable_single_page = true;

	/**
	 * Enable for loop/shop page.
	 *
	 * @var bool
	 */
	public static $enable_loop_page = true;

	/**
	 * Boostrap and shoot.
	 */
	public static function init() {
	
		// Change out of text alt here.
		self::$alt_text = __( 'Coming Soon', 'woocommerce' );

		if ( self::$enable_single_page ) {
			add_filter( 'woocommerce_get_availability_text', array( __CLASS__, 'change_out_of_stock_text' ), 10, 2 );
		}

		if ( self::$enable_loop_page ) {
			add_action( 'woocommerce_after_shop_loop_item_title', array( __CLASS__, 'out_of_stock_alt' ), 10 );
		}

		if ( ! empty( trim( self::$out_of_stock_span_class ) ) && ! empty( trim( self::$out_of_stock_parent_class ) ) ) {
	        // Load JS in WP Footer.
    	    add_action( 'wp_footer', array( __CLASS__, 'js_script' ), 10 );
		}
	}

    /**
     * Changes out of stock text.
     *
     * @param string      $availability
     * @param WC_Product $product
     * @return string
     */
    public static function change_out_of_stock_text( $availability, $product ) {
        if( ! $product->is_in_stock() ) {
            $availability = self::$alt_text;
        }

        return $availability;
    }

    /**
     * Alt text for "out of stock"
     */
    public function out_of_stock_alt() {
        global $product;
        if ( ! $product->is_in_stock() ) {
            printf( '<span class="cx-pekky-coost-alt-text">%s</span>', self::$alt_text );
        }
    }

    /**
     * Js script for manipulation.
     * 
     * @hooked 
     */
    public static function js_script() {
        ?>
        <script type="text/javascript">
            jQuery( document ).ready( function( $ ) {

                /**
                 * Change out of stock text.
                 */
                function pekkyCOOSTAlternator() {
                    let $outOfStock    = $( '<?php echo '.' . self::$out_of_stock_parent_class . ' .' . self::$out_of_stock_span_class; ?>' );
                    let $altOutOfStock = $( '.<?php echo self::$out_of_stock_parent_class; ?> .cx-pekky-coost-alt-text' );

					// Do the change.
					if ( 0 < $outOfStock.length && 0 < $altOutOfStock.length ) {
						$outOfStock.text( $altOutOfStock.html() );
						$altOutOfStock.hide();
					}
                }

                pekkyCOOSTAlternator();
            });
        </script>
        <?php
    }

}

// Launch!!!
Pekky_WC_Change_Out_Of_Stock_Text::init();