I just remade my view in the legacy builder, and now I want to have a map that displays all the (non-filtered) location.
But when I use the builder, it says there is no view to connect the map with.
There is however if you provide the markers in your view with the ID of the map that is on the page.
Is your legacy view currently displaying a map ? What I mean is that you using the map shortcode in your legacy view ? If not then you can use the Fields and Views button in the view to add the map inside the legacy view and then add the markers shortcode as well.
Please let me know if further clarity is needed and we can take it from there.