In general a path-problem query works like this: The QL part computes a graph (the edges predicate) and a set of node pairs (that's your start, end pair in the select). The result interpretation then computes a number of representative paths in the graph for each node pair and shows you these. The default number of paths per result is 4 (IIRC), and you can adjust that to suit your needs by tweaking the VSCode setting codeQL.runningQueries.maxPaths.
It does not make sense to ask for all paths, since there may be an infinite number (when a graph has cycles). We generally impose a limit on the number of paths, since even when the set of paths is finite, it can easily be exponential.

Note that if there are particular points that you want the path to go through then you can use flow states in your data flow config so that you only find paths which go through those points.

Thank you all! That answers my question!