Hi there!
First, I wanted to say that Egypt has been one of my favorite places I have visited to date! Picture a place where you can stop every few hours and there is a temple to view, with so much history, beauty and basically abandoned in the middle of a country with so much heart. This is truly a place everyone should go and visit one day - trust me!
To answer your questions @ck_explorer1000 when I travelled in a multi-day group tour through the country, myself and my friend decided to opt for the sleeper train as we did our research and found the same issues with the bus you did - and our budget was a little more tight than to take the flight.
We were guided by our amazing operator and guide to the train station in Cairo in the evening, and the train station is for sure busy, with tourists and locals alike! After sitting down for some local snacks and a drink, we had to wait a while for the train to come, as our guide mentioned that the train times can be slightly unpredictable. I had a lovely visitor sit with me while we were waiting for the train - picture attached!
When trains were passing by, we noticed that some of them had smashed glass and were getting worried that ours would look the same - but when the train arrived it was really more than we expected in the first place.
As a solo traveller, you will get an entire room to yourself with a bathroom just outside. It is by no means luxurious but for sure better than I had ever guessed. The train is a little old, do not think its a modern train with luxury fittings, but it for sure runs amazing to take you from A-B.
I shared a room with my co-traveller and at first they left the beds as seating so that you could relax and get acquainted. Once dinner was served (which, wow, the food on the train was exceptional!) the host of your train car changes the seats to beds and makes up the bed for you. The night sleep might not have been the best ever, as you hear all the train sounds at night, but it was for sure better than the experience the others in our group had on the night bus!
Breakfast was also served on the train and you could watch the hills and landscapes pass by, with the local people tending to their farms - just watching from the train as live zooms past you.
We ended up in Aswan around 7 am (if I recall correctly) before we were taking to our hotel to freshen up - during the day we had plenty energy to explore the temple of Philea and explore the city so if you are willing to rough it slightly but have an amazing and more down-to-earth- experience, I would choose the train above the flight every day.
PS: Sorry for the long answer, but I hope this was super helpful. I also attached a of the cabin to give you some ideas!