Middle Platonism is like a game of pretend where people imagine there is a separate world of perfect and eternal things that can't be seen or touched. They think that the physical world we live in is just a copy of this perfect world. Sort of like how a drawing of a car is a copy of a real car.
Some people who play this game of pretend believe that we can learn about this perfect world by thinking really hard and using our brains. They think that by doing this, we can find out which things are true and which things are not.
Other people who play this game of pretend believe that we can also learn about the perfect world by looking at the things around us and noticing how everything fits together. They think that by looking at nature and how things work, we can figure out which things are true and which things are not.
Either way, the people who play Middle Platonism believe that there is more to the world than what we can see and touch. And they think that by figuring out what is true in this perfect world, we can better understand the world we live in.