Get-PnPListItemRoleAssignmentDefinitionBindings.ps1

param(
    [Parameter(Mandatory = $true)]
    [string]$ListTitle,

    [Parameter(Mandatory = $true)]
    [int]$ItemId,

    [Parameter(Mandatory = $true)]
    [string]$Path
)

# You'll need to use Connect-PnPOnline before running the script :)

# Stop on first (unhandled) Exception
$ErrorActionPreference = "Stop"

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

# Load role assignments
$roleAssignments = Get-PnPProperty -ClientObject $item -Property "RoleAssignments"

# Array to store output
$rows = @()

# Loop over role assignments, load bindings
foreach($ra in $roleAssignments) {
    $userOrGroupId = $ra.PrincipalId

    # Retrieve the user or group item from the User Information List by its item ID
    $userOrGroupItem = Get-PnPListItem -List "User Information List" -Id $ra.PrincipalId -Fields "Title", "Name", "EMail"

    # Load role definition bindings
    $bindings = Get-PnPProperty -ClientObject $ra -Property "RoleDefinitionBindings"

    # Get role definition binding names as a string array
    $bindingNames = $bindings | Select-Object -Property "Name" -ExpandProperty "Name"

    # Create HashTable of useful properties
    $row = @{
        "Principal Id" = $ra.PrincipalId;
        "Principal Name" = $userOrGroupItem.FieldValues["Title"];
        "Principal Login" = $userOrGroupItem.FieldValues["Name"];
        "Principal Email" = $userOrGroupItem.FieldValues["EMail"];
        "RoleDefinitionBindings" = [string]::Join(", ", $bindingNames);
    }

    # Convert to PSObject and add to $rows with columns in the order specified
    $rows += New-Object psobject -Property $row | Select-Object -Property "Principal Id", "Principal Name", "Principal Email", "RoleDefinitionBindings"
}

# Save data as CSV
$rows | Export-Csv -NoTypeInformation -Path $Path -Force