Hello

Some good advice from Socks Mum. How many weeks is it since he came to you? It can take them a good two or three weeks to fully settle into a cage. But I assume he was a baby hamster and they are usually quite scared and some may just hide away under the bedding. And get in the habit. Their personalities also vary a lot. I had one like this, and I think that starting with taming and socialising will help gradually. However that is tricky if you don't see him. I assume he's sleeping under the pile of bedding in the middle or under the carrot house? Or maybe you're not sure.
I personally don't think there is such a thing as a ghost hamster. Sometimes the most shy hamsters become the most affectionate once they are tamed. It took a bit of a cage adjustment with my shy boy but I wouldn't do that straight away or you'll stress him out as you haven't had him long.
For now, try and feed at around the same time each night - maybe 8pm - make a bit of cage noise while doing it - not a lot obviously but even openning the cage door or tapping it afterwards, can become a familiar sound that means food to them. Assume you give a tiny bit of veg daily? No bigger than his ear so he actually eats it. I would stick with cucumber for now - they like the small. I give a little cube of cucumber around that size - you could also use a tiny broccoli floret - they like that too. Lettuce isn't the best option. But sometimes the smell of the cucumber draws them out so one tip is put it on a separate little dish on the other side of the cage to where he is sleeping (if you know where that is!). So he will have to cross the cage to get it, and on the way back you can offer him something like a rat tube/taxi. They will usually walk into a tube but something tempting at the far end can help - another bit of cucumber, strawberry or tiny bit of cheese.. All smell quite irresistable. Once in the tube you can put your hands over the end and lift it out and transport him to a nearby box or playpen. If the playpen isn't nearby then use the box to transport him to the playpen.
However if he is hiding away and waiting until it's dark to come out and get food, then this could become a habit. So a nightcam could really help here.
You can sit in bed and watch him on your phone via the live footage. See when he comes out and then sneak down. They often look a bit surprised or might freeze, but you could try offering him the tube then - if it's not too late at night. Alternatively watch the footage the next day and work out his routine.
Personally I would consider reducing the amount of bedding for a while and adding a large cork log in the middle so he has something to sit under and doesn't feel timid about the space. Maybe on the left in front of the sprays/near the middle.
But depending on how many weeks it's been I'd give it another week before doing that. Sometimes it's a bit of time and patience. It's very hard at first when you want to see them and handle them.
I have this petcam - it just needs an sd card, connects to wifi. Place it opposite the cage somewhere if you can (I had mine on a pile of books on the back of a living room chair at one point!) It can be difficult to find a place. It helps at first to see you actually have a hamster and you can enjoy watching next day and seeeing what he has been getting up to! The footage next day has coloured areas when there is movement recorded so you can just scroll/scan through to see the times he is in the footage.
Eufy petcam