Get-SharePointVersionHistorySize

<#
.SYNOPSIS
    Estimates storage consumed by version history per library.

.DESCRIPTION
    Walks document libraries in a site and compares total file size
    against current version size, giving a rough estimate of how much
    space old versions are consuming, so you know whether trimming
    version limits is actually worth doing before changing the setting.

.PARAMETER SiteUrl
    URL of the site to check.

.EXAMPLE
    .\Get-SharePointVersionHistorySize.ps1 -SiteUrl https://contoso.sharepoint.com/sites/finance

.NOTES
    Requires PnP.PowerShell.

.AUTHOR
    Shehryar Hassan
#>

param(
    [Parameter(Mandatory)]
    [string]$SiteUrl
)

Connect-PnPOnline -Url $SiteUrl -Interactive
$lists = Get-PnPList | Where-Object { $_.BaseTemplate -eq 101 -and -not $_.Hidden }

$report = foreach ($list in $lists) {
    $items = Get-PnPListItem -List $list -PageSize 500
    $totalVersionSizeMB = 0
    foreach ($item in $items) {
        $versions = Get-PnPFileVersion -Url $item.FieldValues.FileRef -ErrorAction SilentlyContinue
        $totalVersionSizeMB += (($versions | Measure-Object Size -Sum).Sum / 1MB)
    }
    [pscustomobject]@{
        Library           = $list.Title
        ItemCount         = $items.Count
        EstimatedVersionMB = [math]::Round($totalVersionSizeMB, 1)
    }
}

$report | Sort-Object EstimatedVersionMB -Descending | Format-Table -AutoSize