1. If select_the_value
is a true/false field, it will already return true/false, so if(get_field('select_the_value'))
should be enough.
2. If select_the_value
is another kind of field (e.g. checkbox or select), 'TRUE'
must be defined as a field option (ergo be a string), otherwise it won’t match
In other words, this might work like this:
$fieldName = get_field('select_the_value') ? 'select_the_country' : 'select_the_city';
the_field($fieldName, $queried_object);