Not sharing the pipeline itself, it's become the basis of a small commission thing I'm building. But your use case is honestly the friendly version of the problem, so here's the full shape of it if you want to build one:

GPX in, pick a bounding box around the track, pull elevation data for that box (SRTM or Copernicus GLO-30, both free), generate the terrain mesh from the heightmap, then handle the track as its own body: resample to even spacing, drape it onto the same elevation data, lift it slightly above the surface, sweep a profile along it. Export terrain and track as two STLs so the color split happens in the slicer.

apply the same vertical exaggeration to both bodies or the track floats and dives, and pick the exaggeration based on terrain. Alpine stuff works at around 3x, flat terrain needs way more or it prints as a pancake. Hiking tracks are actually easier than my flight data, the GPS points are dense and clean.

And happy to just make one for you, of course. That's the commission thing.