> So what should you do? Just call it My Awesome Notepad and expect users who are searching for Notepad++ to somehow find it?
Yes. Exactly that. You have no entitlement to free publicity based of someone else's hard work growing their own brand.
You could arguably say "Awesome Notepad, a Notepad++ fork" but even here, the trademark holders can demand you to remove the references to their product if they wished. In this specific instance, Given Notepad++ is open source, I suspect the maintainers of Notepad++ might have been okay with this approach. Though it's a little late for that now because the Mac port author has burned any good faith they might have had.
Another option is to gain trust with the Notepad++ maintainers and then request they link to "Awesome Notepad" project site as an endorsed 3rd party port. But again, the Mac port author hasn't taken the right approach to gain any trust there.
So as it stands, "Notepad++ Mac" is intentionally using Notepad++'s trademarks and branding as a way to get publicity quickly. I don't think they're doing it maliciously, but the intent is still dishonest.