For Trailforks to automatically flag a users ride as "sensitive", the unsanctioned or illegal trail has to actually be privately mapped on Trailforks and designated as "hidden". So if it's not in the system, there is nothing we can do. And because of the nature of GPS inaccuracy, especially in the woods on shitty phones, the GPS tracks sometimes are not within the margins to "match" a trail.
For areas that are separated and not intermixed with sanctioned trails, like several you can probably think of on the Shore. Trailforks can mark the entire region as "hidden" and all rides that intersect the polygon of that hidden region are excluded from the heatmap. But automated systems can't catch everything, but at least we try unlike other apps.
If riders are making their sensitive rides public with no discretion, this is ultimately an education and culture problem. Even if automated systems worked 100% of the time, their data would still be public on other platforms.