By his own admission Sandy's guide is very outdated. He plans to update his guide for 2024. I've just returned from walking the Way of Saint Francis from Florence to Rome and I carried the Village to Village guide written by Mathew Harms. It was just released in March and I had it with me when I set off in mid-May. There are GPX tracks available through either guide and also on the St. Francis Facebook group page if you have access. It's a challenging route, but after Assisi not nearly as much. And please don't think that I don't like Sandy's guides. I used two of them last year when walking from London to Rome on the Via Francigena. To the best of my knowledge there isn't presently an app. Have fun planning!