OP, do you know what the "Counting Numbers" are? They are numbers like 1, 2, 3, 4, etc. Mathematically speaking, the set of Counting numbers is an infinite set.

Now suppose I say to you, "Here is an infinite set of numbers, all of which are counting numbers." Does that mean that my set of numbers must contain all counting numbers? No, it doesn't. Look at the set of even numbers, i.e. 2, 4, 6, 8 etc. It is an infinite set of counting numbers, but it's not ALL counting numbers. A set can be infinite without containing everything possible.

Likewise, even if we assume that the universe is infinite, we cannot say that everything physically possible exists.