Obviously fallahn will know it better than anyone but I have used it a little bit. As far as I know the loader itself doesn't really do anything for collision. I'm sure there are ways to code generating the collision boxes in an efficient way but I have always opted to manually put in collision rectangles as a "bounds" layer in the TMX.
I'm just copying and pasting pieces but I gathered a vector of collision boxes like this.
std::vector<sf::FloatRect> mapBounds;
tmx::MapLoader map("maps\\");
std::vector<tmx::MapLayer> mapLayers;
sf::Vector2u mapSize;
void Scene::loadmap(std::string mapName)
{
map.Load(mapName);
mapBounds.empty();
mapLayers = map.GetLayers();
mapSize = map.GetMapSize();
for (const tmx::MapLayer layer : mapLayers)
{
if (layer.name == "Bounds")
{
for (const tmx::MapObject& mapObject : layer.objects)
{
mapBounds.push_back(mapObject.GetAABB());
}
}