Check if the data has been change before saving

I'm trying to send a notification to the process owner everytime the data of process owner is change after saving. I don't want to spam notification everytime the user click the save so I want to check it before saving. The code below always returns false even if I'm changing the value of the process_owner

protected function beforeSave(): void
{
dd($this->record->isDirty('process_owner'));
}