Open Source Routing Machine
This excellent suggestion was made two years ago and so far has received only a handful of votes.
The OSRM works to help you find routes on OSM (OpenStreetMap). This function is already supported in NextCloud.
Cloudron supports NextCloud, which has a maps module, using OSM. The maps module needs a routing engine for it to help you find a way from A to B. OSRM would provide such an engine.
There is a Docker:
If you go into NextCloud's additional settings, you can find this: