For a document by its item id download all versions incl. the current.

FileVersionDownload.ps1

param (
    [string]$Url,
    [string]$Listname,
    [int]$ItemId,
    $Credentials,
    [string]$DownloadFolder
)

if ($Credentials -eq $null)
{
    $Credentials = Get-Credential
}

Connect-PnPOnline -Url $Url -Credentials $Credentials

$item = Get-PnPListItem -List $Listname -Id $ItemId

$versionString = $item["_UIVersionString"]
$createdCurrent = $item["Modified"].ToString("dd.MM.yyyy-HH:mm:ss") # when this version was created ;-)
$createdByTitleCurrent = $item["Author"].LookupValue
$createdByEmailCurrent = $item["Author"].Email

$filename = $item["FileLeafRef"]
$fileUrl = $item["FileRef"]

$fileHistoryFile = $DownloadFolder + "\History for " + $filename + ".txt"

"Version;Created;CreatedBy;CreatedByEmail" | Out-File -FilePath $fileHistoryFile -Force

Get-PnPFile -Url $fileUrl -Path $DownloadFolder -Filename ($versionString + " - " + $filename) -AsFile -Force

$fileVersionCollection = Get-PnPFileVersion -Url $fileUrl

foreach ($fileVersion in $fileVersionCollection)
{
    $createdBy = Get-PnPProperty -ClientObject $fileVersion -Property CreatedBy
    $createdByTitle = $createdBy.Title
    $createdByEmail = $createdBy.Email

    $versionLabel = $fileVersion.VersionLabel
    $created = $fileVersion.Created.ToString("dd.MM.yyyy-HH:mm:ss")

    "$versionLabel;$created;$createdByTitle;$createdByEmail" | Out-File -FilePath $fileHistoryFile -Append

    Write-Host $versionLabel

    $stream = $fileVersion.OpenBinaryStream()

    Invoke-PnPQuery

    $downloadFile = $DownloadFolder + "/" + ($versionLabel + " - " + $filename)

    $fileStream = New-Object System.IO.FileStream($downloadFile, [System.IO.FileMode]::OpenOrCreate)
    $stream.Value.CopyTo($fileStream)
    $fileStream.Dispose()
}

Write-Host $versionString

"$versionString;$createdCurrent;$createdByTitleCurrent;$createdByEmailCurrent" | Out-File -FilePath $fileHistoryFile -Append

Write-Host "Done."