How to get a Google Maps route URL
Maps to GPX needs a Google Maps directions URL, not a single place page. The URL should represent a route from one point to another.
A good link usually opens the same route when pasted into a private browser window, with the start, destination, and route line already visible.
Use a directions link
A supported link usually contains /maps/dir/ after it is expanded. If the link only opens a restaurant, shop, or landmark page, create directions first and share that route instead.
Short links are supported
Links starting with maps.app.goo.gl can work as long as they expand to a directions route. The service expands short links before reading origin, destination, and embedded coordinates.
When a link fails
Open the route in Google Maps again, confirm that both start and destination are visible, then copy the share link again. Some app-specific links may omit information needed for GPX generation.
Multiple stops
Routes with stops can work when Google Maps includes those stops in the shared directions URL. If a stop disappears after sharing, add it again in Google Maps and create a fresh link.
Bike routes and local roads
Google Maps route choices may change by transport mode, region, and current data. Before converting, confirm the route uses roads or paths that are appropriate for cycling in your area.