You can do this by adding another PowerShell task(to create a bug) at the end of your release definition if the task before fails. Select the option "Only when a previous task has failed".
Your PowerShell script to create a bug should look something like this:
$witType="Bug"
$witTitle="title"
$u="https://account.visualstudio.com/DefaultCollection/project/_apis/wit/workitems/`$$($witType)?api-version=1.0"
$body="[
{
`"op`": `"add`",
`"path`": `"/fields/System.Title`",
`"value`": `"$($witTitle)`"
}
]"
$user = "username"
$token = "PAT"
$base64AuthInfo = [Convert]::ToBase64String([Text.Encoding]::ASCII.GetBytes(("{0}:{1}" -f $user,$token)))
$result=Invoke-RestMethod -Method PATCH -Uri $u -Headers @{Authorization=("Basic {0}" -f $base64AuthInfo)} -ContentType "application/json-patch+json" -Body $body