system/Model.php
public function updateBatch(array $set = null, string $index = null, int $batchSize = 100, bool $returnSQL = false)
	{
		if (is_array($set) && $this->skipValidation === false)
		{
			foreach ($set as $row)
			{
				if ($this->validate($row) === false)
				{
					return false;
				}
			}
		}

		return $this->builder()->updateBatch($set, $index, $batchSize, $returnSQL);
	}
public function updateBatch(array $set = null, string $index = null, int $batchSize = 100, bool $returnSQL = false)
	{
		if (is_array($set) && $this->skipValidation === false)
		{
			foreach ($set as $row)
			{
				if ($this->validate($row) === false)
				{
					return false;
				}
			}
		}

		return $this->builder()->updateBatch($set, $index, $batchSize, $returnSQL);
	}
Update_Batch

Compiles an update string and runs the query

@param array   $set       An associative array of update values
@param string  $index     The where key
@param integer $batchSize The size of the batch to run
@param boolean $returnSQL True means SQL is returned, false will execute the query

@return mixed    Number of rows affected or FALSE on failure
@throws \CodeIgniter\Database\Exceptions\DatabaseException