Use the code snippet to dynamically populate a select field's choices in ACF.

Dynamically populate a select fields choices in ACF

//dynamically populate a select fields choices
function acf_load_category_field_choices( $field ) {
    
    // reset choices
    $field['choices'] = array();
    
    
    // get the textarea value from options page without any formatting
    $choices = get_categories();

	$i = 0;
	$len = count($choices);
	$choicestring = '';
	
	foreach( $choices as $choice ) {
		if ($i == $len - 1) {
			$choicestring .= $choice->slug;
		}else{
			$choicestring .= $choice->slug.'*#@';
		}
		$i++;
	}

    // explode the value so that each line is a new array piece
    $choicestring = explode("*#@", $choicestring);

    // remove any unwanted white space
    $choices = array_map('trim', $choicestring);

    
    // loop through array and add to field 'choices'
    if( is_array($choices) ) {
        
        foreach( $choices as $choice ) {
            
            $field['choices'][ $choice ] = $choice;
            
        }
        
    }
    

    // return the field
    return $field;
    
}

add_filter('acf/load_field/name=slider_category', 'acf_load_category_field_choices');