Any example of a major Android-only app for the US?

You said "As a developer", not "As a major developer".

Beeper Mini, Fortnight, several Google apps.

Not gonna lie, all of these examples are pretty weak because all of them are in circumstances that 99% of developers are never going to be in.

Beeper Mini replicates native iOS functionality - it's obvious why it can only exist as an Android-only app.

Fortnite is the product of a massive studio, whose decision of not publishing it on iOS was deliberate as part of their anti-monopoly lawsuits. They can easily afford to do it because Epic Games has other revenue sources, alongside with running Fortnite on pretty much every other platform imaginable.

Google doesn't really cash in on their more niche apps, publishing them on iOS is unlikely to change anything for them. However, not choosing to publish them gives Android - their own product - a tiny boost in appeal due to exclusive functionality.

Keyword: major.

Fortnight is the only example, and it's on its way to SCOTUS. Google apps, which one?

Fortnite has an iOS version. They just stopped being able to update it because of Epic's shenanigans.

Major? Probably not many; once you're a major developer, you'll go wherever there's money to be made. That doesn't mean it isn't possible to skip iOS—but unless you have some philosophical objection to it, there's no reason why you would.

But anyway, you said "As a developer..." not "As a major developer...".