The Flash briefly appears in [the alternate universe story] Kingdom Come when the book is establishing its world’s status quo. Described as living “between the ticks of a second,” the Scarlet Speedster has turned his home of Keystone City into a crime-free paradise. He’d pushed himself so hard and gotten so fast that he was effectively omnipresent and could easily stop any disturbance before it began. However, in the process, Wally West had stopped slowing down to do human things like talk to people or sleep.

https://www.cbr.com/wally-west-flash-kingdom-come-darkest-timeline/