In the season 6 episode of The Flash TV series, we see that Flash enters a black hole and returns back. since it is scify I can understand him going inside and speed force aura protecting him, but how does he turn around and come back? Doesn't he need a medium to run/turn around?
As indicated in the comments, it's the speedforce. It's a Macguffin that's used to move the plot forward.
When we're talking superheroes and movies (or comics) you just have to suspend disbelief because the bulk of what happens is just not possible. If you think about it, without the Macguffin, Barry would probably burn to a crisp the first time he ran at high speeds - never mind the damage he would do to himself and others by punching or kicking people. Shoot, just running past people at high speeds would provide damage to them (this is shown, but minimized, on the show).