How to set up alert on failed Windows task

There's definitely other threads on this with more info.
There's an out-of-the-box monitor for windows tasks, it only cares about the top level folder, and will only trigger based on if the task gives a sign it failed. Which is down to the author and very much not universal.
There's some powershell equivalents for additional info, which can be unpleasant to deal with for security