The Karman Line is 100 km (62 miles). Any lower than that, and Earth’s atmosphere must be overcome to maintain orbit. The lowest an object can be to maintain orbit without propulsion is ~150 km (90 miles).
Even the ISS has to perform regular boost maneuvers to maintain its orbit. Earth’s atmosphere doesn’t just stop existing at an arbitrary number.
The Karman Line is the universally-accepted altitude at which space begins, but atmosphere does still exist there.
Interesting. I have always wondered where gravity was no longer a factor. When that guy jumped out of the capsule, he was in space, or so I thought..