my take on convert .xlsx to .CSV in Powershell using Excel COM (Windows only)

CustomConvert-XlsxToCsv.ps1

$step = ''

function CustomConvert-XlsxToCsv
{
    param(
        [Parameter(Mandatory)]$XlsxFile,
        [string]$Sheet = 'Sheet1',
        [string]$CsvFile,
        [switch]$Test
    )
    
    $script:step = "init variables";

    $filebase = [System.IO.Path]::GetFileNameWithoutExtension($XlsxFile);
    $dataDir = $PWD.Path;
    if ([System.IO.Path]::IsPathRooted($XlsxFile))
    {
        $dataDir = Split-Path -Parent $XlsxFile;
    }
    else {
        $XlsxFile = Join-Path $dataDir $XlsxFile;
    }

    if ($CsvFile -eq '') {
        $CsvFile = "$dataDir\$filebase.csv";
    }
    elseif (-not [System.IO.Path]::IsPathRooted($CsvFile))
    {
        $CsvFile = Join-Path $dataDir $CsvFile;
    }

    $script:step = "create COM automation object: New-Object -ComObject Excel.Application";
    if ($Test) {
        [void]($objExcel = $global:objExcelConvertXlsx);
        if (!($objExcel)) { throw 'create $global:objExcelConvertXlsx before running in test mode' }
    }
    else {
        [void]($objExcel = New-Object -ComObject Excel.Application);
        $objExcel.Visible = $false;
    }

    $script:step = "opening: objExcel.Workbooks.Open($XlsxFile)"
    [void]($workbook = $objExcel.Workbooks.Open($XlsxFile));

    if ($Test) { $workbook.sheets | Select-Object -ExpandProperty Name; }

    [void]($worksheet = $workbook.sheets.item($Sheet));

    if (Test-Path $CsvFile) { del $CsvFile -Verbose:$Test; }

    $script:step = "Saving --$CsvFile--";
    $worksheet.SaveAs($CsvFile, [Microsoft.Office.Interop.Excel.XlFileFormat]::xlCSVWindows);
    Write-Warning "Saved --$CsvFile--";

    # .NET enums are auto-converted, but looks like COM enums are not.  This doesn't work: 
    # $worksheet.SaveAs("$dataDir\$filebase.csv", 'xlCSVWindows')

    if ($Test) { return; }

    $script:step = "cleanup";
    $objExcel.Quit();
    [System.Runtime.Interopservices.Marshal]::ReleaseComObject($objExcel);
    Remove-Variable objExcel;
}

try {
    #cd C:\code\archive\2019-project1\hours
    #CustomConvert-XlsxToCsv -XlsxFile AppSchedule.xlsx # exports Sheet1
    #CustomConvert-XlsxToCsv -XlsxFile AppSchedule.xlsx -Sheet exceptions -CsvFile AppSchedule-Exceptions.csv

    CustomConvert-XlsxToCsv -Sheet schedules -XlsxFile C:\code\archive\2019-project1\hours\AppSchedule.xlsx
}
catch {
    Write-Warning "last step before error: $step";
}
#finally {}