`Maybe a` all on its own doesn’t have a monoid instance. There are a few possible semantics it can have.

If `a` is a monoid, then there is an instance for `Maybe a`. It’s worth trying to guess how this is defined in base if you haven the seen it.

Apart from `First`, there is another new type called `Last` that gives different monoid semantics for `Maybe`. You can always look it up with hoogle, but the name is a good hint at how it works if you want to guess...