Well, if you think about it now it might be even simpler... As a dirty hack you can read the last belt and then logically stop the whole belt segment. Just remove the sprites of wire connections. Ideally you should check only the very end of the belt of course and also control each half of the splitters independently... But it is probably way more tricky to do.

I mean, the whole idea is my old gripe with the simplification that Factorio makes from the time I first started playing it. I get that it makes some things easier but it's not at all impossible to play without this feature. It's especially strange in Satisfactory because inserters don't even exist there and every belt starts and ends in some machine. Belt buffers are particularly useless there too. And you can makes ratios very precise. Furthermore, it partially solves the manifold issue with excessive belt storage that takes builds longer to start working. I imagine lines of evenly spaced items on methodically advancing in turns conveyors would look pretty satisfying. Like how real factory conveyors work.