here is powershell script on how to get list of files from changesets associated with one tfs task

  
$dllPath = "C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\Common7\IDE\CommonExtensions\Microsoft\TeamFoundation\Team Explorer"
Add-Type -Path "$dllPath\Microsoft.TeamFoundation.Client.dll"
Add-Type -Path "$dllPath\Microsoft.TeamFoundation.WorkItemTracking.Client.dll"
Add-Type -Path "$dllPath\Microsoft.TeamFoundation.VersionControl.Client.dll"

# Connect to TFS
$tfsUri = "https://tfs2.domain.net/tfs/project"
$username = "DOMAIN1\user1"     # or just "your-username" if no domain
$password = "-password-here"

# Create secure credentials
$securePassword = ConvertTo-SecureString $password -AsPlainText -Force
$credentials = New-Object System.Net.NetworkCredential($username, $securePassword)

# Create TFS connection using credentials
$uri = New-Object System.Uri($tfsUri)
$tfs = New-Object Microsoft.TeamFoundation.Client.TfsTeamProjectCollection($uri, $credentials)

$tfs = [Microsoft.TeamFoundation.Client.TfsTeamProjectCollection]::new($tfsUri)
$tfs.EnsureAuthenticated()

# Get services
$workItemStore = $tfs.GetService([Microsoft.TeamFoundation.WorkItemTracking.Client.WorkItemStore])
$versionControl = $tfs.GetService([Microsoft.TeamFoundation.VersionControl.Client.VersionControlServer])

# Get work item (replace with your Task ID)
$workItem = $workItemStore.GetWorkItem(29574)

$dict=@{}
# Loop over links to find associated changesets
foreach ($link in $workItem.Links) {
    if ($link -is [Microsoft.TeamFoundation.WorkItemTracking.Client.ExternalLink] -and
        $link.ArtifactLinkType.Name -eq "Fixed in Changeset") {

        $csId = [int]($link.LinkedArtifactUri -replace ".+changeset\/", "")
        $changeset = $versionControl.GetChangeset($csId)

        #Write-Output "Changeset $csId"
        foreach ($change in $changeset.Changes) {
            #Write-Output " - $($change.Item.ServerItem)"
            $key=$change.Item.ServerItem
            if (-not $dict.ContainsKey($key)) {
                $dict[$key] = $csId
}
            }
    }
}
foreach ($key in $dict.Keys) {
    #Write-Output "$key : $($dict[$key])"
    Write-Output $key
    Add-Content -Path "output.txt" -Value $key
}