PowerShell Azure Function that takes an array with desired objects as child arrays as an input and outputs a single array object with child items only.

ConvertTo-Merged.ps1

using namespace System.Net

# Input bindings are passed in via param block.
param($Request, $TriggerMetadata)

# Author: Daniel Ferreira (@daniel0x00)  
# License: BSD 3-Clause

# Expected input POST Body schema:
# {
#  "InputObject": ["<object>","<object>"],                 --> input array object.
#  "ExpandProperty": "<string>",
#  "MergeProperty": "<string>"
# }

## EXAMPLE:

# INPUT:
# {
#   "ExpandProperty": "ContentData",
#   "MergeProperty": "records",
#   "InputObject": [
#     {
#       "ContentData": {
#         "records": [
#           {
#             "time": "2020-12-26T12:12:58.7181726Z",
#             "operationName": "MICROSOFT.COMPUTE/DISKS/DELETE",
#             "category": "Administrative",
#             "resultType": "Success",
#             "resultSignature": "Succeeded.",
#             "durationMs": "0",
#             "level": "Information"
#           }
#         ]
#       },
#       "Properties": {
#         "x-opt-sequence-number": 1662941,
#         "x-opt-offset": "811766696840",
#         "x-opt-enqueued-time": "2020-12-26T12:22:03.399Z"
#       },
#       "SystemProperties": {
#         "EnqueuedTimeUtc": "2020-12-26T12:22:03.399Z",
#         "Offset": "811766696840",
#         "PartitionKey": null,
#         "SequenceNumber": 1662941
#       }
#     },
#     {
#       "ContentData": {
#         "records": [
#           {
#             "time": "2020-12-26T12:10:51.7568646Z",
#             "category": "Administrative",
#             "resultType": "Success",
#             "resultSignature": "Succeeded.",
#             "durationMs": "0",
#             "level": "Information",
#           }
#         ]
#       },
#       "Properties": {
#         "x-opt-sequence-number": 1662942,
#         "x-opt-offset": "811766699280",
#         "x-opt-enqueued-time": "2020-12-26T12:22:06.213Z"
#       },
#       "SystemProperties": {
#         "EnqueuedTimeUtc": "2020-12-26T12:22:06.213Z",
#         "Offset": "811766699280",
#         "PartitionKey": null,
#         "SequenceNumber": 1662942
#       }
#     }
#   ]
# }

# OUTPUT:
# [
#   {
#     "operationName": "MICROSOFT.COMPUTE/DISKS/DELETE",
#     "durationMs": "0",
#     "resultType": "Success",
#     "time": "2020-12-26T12:12:58.7181726Z",
#     "level": "Information",
#     "resultSignature": "Succeeded.",
#     "category": "Administrative"
#   },
#   {
#     "operationName": "MICROSOFT.COMPUTE/VIRTUALMACHINES/DELETE",
#     "durationMs": "0",
#     "resultType": "Success",
#     "time": "2020-12-26T12:10:51.7568646Z",
#     "level": "Information",
#     "resultSignature": "Succeeded.",
#     "category": "Administrative"
#   }
# ]


# Return:
$StatusCode = [httpstatuscode]::OK
# Set output vars:
$Output = [string]::empty

try {
    # Parse input:
    $InputObject = $Request.Body.InputObject
    $ExpandProperty = $Request.Body.ExpandProperty
    $MergeProperty = $Request.Body.MergeProperty

    # Const:
    $JSONDepth = 10 
   
    ## Output:
    $Output = @(($InputObject | Select-Object -ExpandProperty $ExpandProperty).$MergeProperty) | ConvertTo-Json -Depth $JSONDepth -AsArray -Compress
}
catch {
    Write-Verbose "Catch triggered: $_" -Verbose
    $StatusCode = [httpstatuscode]::InternalServerError
}
finally {
    Push-OutputBinding -Name Response -Value ([HttpResponseContext]@{
        ContentType = 'application/json'
        StatusCode = $StatusCode
        Body = $Output
    })
}