My point, however, was that this is not obvious for anyone starting with React.

This is caused by the fact that React is "no batteries included", which means that you have to find the right batteries at a moment when you lack all knowledge about batteries in the first place. You search "how to send to backend" and saga's pop up, explaining why they are better than useEffect or redux or whatever (at a moment you may not even know useEffect or its downsides).

Compare that to Rails which has "all batteries included" (and which is a nightmare in itself, too, though), where all those choices are made for you. You can choose to ignore Rails' testing suite and instead erect an rspec setup next to it, but you'll do so consiously. Because that moment when you asked yourself "how do I test in rails" the One True Way was there, configured, ready for use and documented.

Both have tradeoffs and pros and cons. But the React community (with tutorials, this weeks best practices, breakspeed iterations of tooling) is not helping here. At all.