US rocketry has a tradition of making second stages dispose of themselves after their work is done. AFAIK no regulatory body enforces this - but launch providers usually do it anyway.
A common way to do that is to perform an extra burn and tip the second stage's orbit into the atmosphere - so that it burns up in a controlled manner. That's what's done on Starlink launches - the most common type of US launch.
Other countries may choose not to do that, because the second stage has to be designed to allow for those extra burns, and the fuel used cuts straight into the performance margins.
> Are they in the same orbit as the satellites?
Not exactly. Most larger satellites nowadays carry their own fuel and engines, and perform orbital adjustments and station-keeping. Which has a way of putting distance between them and the second stages. They might end up in the same orbital plane, but not the same orbit.
For some satellite types, the second stage only gets the satellite to a transfer orbit - and the satellite itself gets to the deployment orbit from there under its own power.
A common way to do that is to perform an extra burn and tip the second stage's orbit into the atmosphere - so that it burns up in a controlled manner. That's what's done on Starlink launches - the most common type of US launch.
Other countries may choose not to do that, because the second stage has to be designed to allow for those extra burns, and the fuel used cuts straight into the performance margins.
> Are they in the same orbit as the satellites?
Not exactly. Most larger satellites nowadays carry their own fuel and engines, and perform orbital adjustments and station-keeping. Which has a way of putting distance between them and the second stages. They might end up in the same orbital plane, but not the same orbit.
For some satellite types, the second stage only gets the satellite to a transfer orbit - and the satellite itself gets to the deployment orbit from there under its own power.