To remotely query Garance data using SPARQL: the SPARQL endpoint is located at https://sparql.archives-nationales.culture.gouv.fr/garance/sparql.
The SPARQL endpoint also has a user interface: https://sparql.archives-nationales.culture.gouv.fr/garance. There you will find example queries (click the "Examples" button). You can share your query URLs (click the "Share" button).
Finally, we offer an experimental tool that allows for a quick search by entity name (value of the rdfs:label property), and then, after selecting a result and dragging it into the right-hand window, visualizing the graph in which the selected entity is located (by clicking on the icons to the right of the rectangle representing the entity). This tool is available at the following address, currently without associated documentation: https://sparql.archives-nationales.culture.gouv.fr/garance/graph-explorer/.