Customize WP Job Manager wp_editor arguments

functions.php

<?php

add_filter( 'submit_job_form_wp_editor_args', 'smyles_submit_job_form_wp_editor_args' );

function smyles_submit_job_form_wp_editor_args( $args ){
    // @see https://github.com/Automattic/WP-Job-Manager/blob/master/templates/form-fields/wp-editor-field.php#L2
    // change quicktags to true
	$args['quicktags'] = true;
    
	// change rows to 10 (default is 8)
    $args['textarea_rows'] = 10;
	
	// Add underline to TinyMCE toolbar @see https://www.tinymce.com/docs/advanced/editor-control-identifiers/#toolbarcontrols
	// https://www.tiny.cloud/docs/tinymce/6/basic-setup/#toolbar-configuration
	$args['tinymce']['toolbar1'] = 'bold,italic,underline,|,bullist,numlist,|,link,unlink,|,undo,redo';
	
  	return $args;
}

functions_adv_toolbar.php

<?php

// Show "advanced toolbar by default"

add_filter('tiny_mce_before_init', function($init_array) {
    // Show the second toolbar by default
    $init_array['wordpress_adv_hidden'] = false;
    return $init_array;
});

See the defaults for WP Job Manager WP Editor field here:
https://github.com/Automattic/WP-Job-Manager/blob/master/templates/form-fields/wp-editor-field.php#L18

More examples can be found below, as well as specifics and recommendations around what to use for toolbars:
https://gist.github.com/tripflex/5e9024f7a949c423e8be3daea290e6c4