->orderBy(["FIELD(step, 'star', 'person', 'team')" => true]) is OK, but I didn't look at the underlying code carefully. . . But it should solve the problem

/**
     * @param array $columns
     * @return string the ORDER BY clause built from [[Query::$orderBy]].
     */
    public function buildOrderBy($columns)
    {
        if (empty($columns)) {
            return '';
        }
        $orders = [];
        foreach ($columns as $name => $direction) {
            if ($direction instanceof Expression) {
                $orders[] = $direction->expression;
            } else {
                $orders[] = $this->db->quoteColumnName($name) . ($direction === SORT_DESC ? ' DESC' : '');
            }
        }

        return 'ORDER BY ' . implode(', ', $orders);
    }

This is a method to generate an orderby statement, so true has no real effect, but it is not equal to SORT_DESC and then becomes empty,

The more official way of writing it is like this:

orderBy([new Expression("FIELD(step, 'star', 'person', 'team')")])