A search function could work, but it would need to be designed carefully to be as easy to use as a folder structure, or even the old "cloud and local" model. For example, it used to take just one tap to switch between my half-dozen favourite routes (or to select one of them) and my complete set of 100+ routes (with a further swipe-and-tap to select one of them).

I‌f you can't/won't give us the folders we're asking for, how about a "tap to star" function which we can apply to flag our favourite routes so that these automatically appear at the top of the (now incredibly long) list?‌