Don’t get too excited people. Except for entertainment purpose, existentialism, and particularly solipsism, is worthless hokum and provably so.
As for solipsism, I know I exist so your solipsism is false, and I know people existed before I was born (as my mom made me, and I do not remember anything before then) so my solipsism is also false. Anyone can also easily disprove my solipsism by killing me, and seeing that the world doesn’t disappear.
For other brands of existentialism:
If the 'dream' is voluntary and it us who generate it, then how do we explain that in the dream we can be surprised, that we don’t know the future and that we cannot make things happen at will?
So the dream must be something that happens to us, but then it must come from somewhere other than our mind, and so our mind is not the only thing that exists.
If you ever meet a solipsist or an existentialist, ask them to prove their position by stepping in front of a bus. According to them the bus doesn’t exist, and it is only a figment of their imagination, right?
See how fast they become realists.