Load JSON file into SQL Server Table with Powershell

I am trying to load a JSON file (output from Mongo's Export-MdbcData) into a SQL Server table using Powershell. The example JSON file data is as follows:

{ "code" : "0088", "name" : "BUTTON", "detail" : { "quantity" : 1 } }
{ "code" : "0081", "name" : "MATTERHORN", "detail" : { "quantity" : 2 } }
{ "code" : "0159", "name" : "BANKSTON", "detail" : { "quantity" : 1 } }

In the Powershell script below, the file is read into an array and the array is converted into a datatable to load into a SQL server table. Is there a better/faster way to read in the JSON file? With a small input file, it only takes seconds to load the data but with more than 4M records, it is taking hours for the whole process.

$encoding = [System.Text.Encoding]::UTF8    
$output = [System.Collections.ArrayList]::new()

foreach ($line in [System.IO.File]::ReadLines($pathToJsonFile, $encoding)) 
{
    $json = $line | ConvertFrom-Json 
    foreach ($detail in $json.detail) 
    {
       [void]$output.Add(
                          [pscustomobject]@{
                                      code = $json.code
                                      name = $json.name
                                      quantity = $detail.quantity
                                    }
                        )
    } 
} 
$dataTable = [System.Data.DataTable]::new()
$dataTable = $output | ConvertTo-DataTable
.
.

UPDATE:
I modified the script using @Charlieface's suggestion and removed the inner foreach statement to see if it will speed it up more. It loaded 4M+ records in about 17 minutes. I used batchsize = 80K and each insert iteration took about 14 seconds. However, comparing to a CSV file input with the same batch size and record count, the insert iteration takes about 3 seconds. I'm guessing the parsing of the JSON takes longer than a delimited file.

foreach ($line in [System.IO.File]::ReadLines($pathToJsonFile, $encoding)) 
{
    $json = $line | ConvertFrom-Json;
    [void]$dataTable.Rows.Add($json.code, $json.name, $json.detail.quantity);
    $i++; 
    if (($i % $batchsize) -eq 0) { 
        $bulkcopy.WriteToServer($dataTable) 
        Write-Host "$i rows have been inserted in $($elapsed.Elapsed.ToString())."
        $datatable.Clear() 
    }

}

Might be faster to just create and add the data directly to the datatable, and not use ArrayList or pscustomobject

$dataTable = [System.Data.DataTable]::new();
[void]$dataTable.Columns.Add('code', [string]);
[void]$dataTable.Columns.Add('name', [string]);
[void]$dataTable.Columns.Add('quantity', [int]);

$encoding = [System.Text.Encoding]::UTF8;

foreach ($line in [System.IO.File]::EnumerateLines($pathToJsonFile, $encoding)) 
{
    $json = $line | ConvertFrom-Json;
    foreach ($detail in $json.detail) 
    {
        [void]$dataTable.Rows.Add($json.code, $json.name, $detail.quantity);
    }
}

You may also want to pre-allocate the datatable capacity to some large enough capacity to prevent resizing of the underlying array.

$dataTable.MinimumCapacity = 4100000;

<!-- language-all: sh -->

Assuming you have enough memory, you can greatly speed up your processing as follows:

$dataTable =
  '[' + (Get-Content -Raw -Encoding utf8 $pathToJsonFile) + ']' |
    ConvertFrom-Json |
    ForEach-Object {
      foreach ($detail in $_.detail) { 
        [pscustomobject]@{
          code = $_.code
          name = $_.name
          quantity = $detail.quantity
         }
      }
    } |
    ConvertTo-DataTable