Go through an Error Record recursively and get all exceptions and messages

Resolve-Error.ps1

function Resolve-Error {
[OutputType([object],[string])]  # <-- by default [object], and [string] with AsString 
[CmdletBinding()]
param (
    [Parameter(ValueFromPipeline, Mandatory)]
    [ValidateNotNull()]
    $ErrorRecord,

    [switch]$AsString
)

$List = [System.Collections.Generic.List[object]]::new()

if ($ErrorRecord.psobject.Properties.Name.Contains('Exception')) {
    $List.Add([pscustomobject]@{
        Level   = 'Level0'
        Target  = $ErrorRecord.Exception.TargetSite.Name
        Message = $ErrorRecord.Exception.Message
    })
}

$InnerException = $ErrorRecord.Exception.InnerException
$i = 1
while ([bool]$InnerException) {
    if ($InnerException.Message) {
        $List.Add([pscustomobject]@{
            Level   = "Level$i"
            Target  = $InnerException.TargetSite.Name
            Message = $InnerException.Message
        })
    }
    $i++
    $InnerException = $InnerException.InnerException
}

if ($List.Count -ge 1) {
    $ToStringMethod = {
        if ($this.Target) {$Target = " .$($this.Target)() -"}
        else              {$Target = [string]::Empty}
        '{0} |{1} {2}' -f $this.Level,$Target,$this.Message
    }
    $List | Add-Member -MemberType ScriptMethod -Name ToString -Value $ToStringMethod -Force
}

# reverse the list, start from the last (inner-most) exception and then move up to the (outer) exception
$List.Reverse()

if ($AsString) {($List | foreach {$_.ToString()} | Out-String).Trim()}
else           {Write-Output $List.ToArray()}
}