I have found high-quality pay-once apps with no advertising, and I've done it with minimal effort. Unfortunately, it won't do any good to recommend them to you

I have found high-quality pay-once apps with no advertising, and I've done it with minimal effort. Unfortunately, it won't do any good to recommend them to you, or their developers, because none of them are games, and the apps are so niche that nearly nobody on HN will want to purchase them anyway. But they do exist; they're on the Play Store, hidden in plain sight.