The irony here is that business co-founders actually have at their disposal more and better tools to test a business idea without need of a technical co-founder

The irony here is that business co-founders actually have at their disposal more and better tools to test a business idea without need of a technical co-founder than ever before in history. The smart ones always sold before they built, maybe with a landing page. Now they can also test simple apps while having essentially no coding skills themselves. Obv this does not work in hardware and multiple other domains where complexity grows. But the business co-founders asking for technical co-founders for an app are actually signalling that they are either poorly informed or simply don't want to build with the skills they already have.