Btw, do you know how to save the URL to a property of AudioProcessorValueTreeState, so it will be saved and called for reopening a project? I tried to save URL to a property but it only accept juce::var, not URL.
You can serialize it to a string. However it won’t be accessible anymore this way after the app restarted. Unfortunately JUCE made access to URL’s bookmark data private which is the thing you’d really want to serialize. See Make URL::bookmark publicly accessible