I am traveling alone from Rome to Cortona in August 2019. I have 4 days to get to Cortona. Please suggest where is most beautiful to stay over and visit along the way using the train. Thank you so much.
Do you mean you want to take 4 days to get to Cortona and are looking at what stops to do along the way?
Or that you will have 4 days in Cortona? Since Cortona is about 3 hours or less from Rome by train (less by car), then you could theorteically not make stops along the way at all.
But if you want to make the stops, then I would suggest a stop in Orvieto for a night. It's the only one I can recommend from personal experience along the train line Rome-Cortona. I would suggest from Cortona to make day trips to Arezzo and Perugia.