Json object oddities with New-UDAutocompleteOption

Well, converting your $EventData to JSON works for the UDToast - but for whatever reason, something with the -OnChange trigger is causing this. You could also access the Value with $EventData.Value, predictably.

New-UDAutocomplete -Label 'Select' -Options $STCompOptions -OnChange {
  Show-UDToast (ConvertTo-Json $EventData) -Duration 100000
} -FullWidth