Yes, because friction depends on the air density. You can think of this as the molecules in the air colliding with a moving object and pushing it backwards, thus slowing it. If there are fewer molecules, there is less friction and the object can move faster with the same thrust.
Thrust itself decreases because there are also fewer molecules to push against, so it can get quite complicated if you want to account for everything. But overall it is easier to fly faster higher up in the atmosphere. Also, atmospheric currents are important.
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Yes, because friction depends on the air density. You can think of this as the molecules in the air colliding with a moving object and pushing it backwards, thus slowing it. If there are fewer molecules, there is less friction and the object can move faster with the same thrust.
Thrust itself decreases because there are also fewer molecules to push against, so it can get quite complicated if you want to account for everything. But overall it is easier to fly faster higher up in the atmosphere. Also, atmospheric currents are important.
There is a useful discussion here: https://aviation.stackexchange.com/questions/57209/how-does-...