'In' is the only correct preposition to use in the sense of "x amount of time from now" - in other words, looking forward to a point in the future. For example, "I'll be home in half an hour" or "I'll call you back in five minutes". "After + time" has a different use: it refers to an amount of time following another point. It's often used in the past. For example, "After five hours climbing the hill, they finally reached the top".

“In” is natural. Natural examples of “after” would be I’ll call you sometime after 3. I’ll call you after she gets here. I’ll call after two hours have passed.

In the US and Canada "in" is definitely what a native speaker would say. If a native speaker said "after" they would mean at some point after the time period has elapsed.

Both are natural