Consider an inertial reference frame.

In this coordinate system
1. nothing can accelerate.
2. there is no inertia.
3. objects with no forces acting on them
have no acceleration.
4. inertial mass depends on your elevation.

In an inertial reference frame, the following statements hold true:

1. Nothing can accelerate: In an inertial reference frame, objects do not experience any acceleration unless acted upon by external forces. This means that if an object is at rest, it will continue to stay at rest, and if it is in motion, it will continue to move with a constant velocity in a straight line unless acted upon by an external force.

2. There is no inertia: Inertia is the property of an object to resist any change in its state of motion. In an inertial reference frame, objects still possess inertia, but they will not exhibit any change in their motion unless acted upon by external forces. In other words, objects will maintain their state of rest or constant velocity due to their inertia.

3. Objects with no forces acting on them have no acceleration: In an inertial reference frame, if there are no external forces acting on an object, it will not experience any acceleration. This means that its velocity will remain constant, either zero if it was at rest or a constant non-zero value if it was already in motion.

4. Inertial mass depends on your elevation: The statement that inertial mass depends on elevation is not accurate. Inertial mass is an inherent property of an object and does not depend on the elevation or gravitational field strength. Inertial mass refers to a measure of an object's resistance to acceleration when subjected to a force. It determines how an object responds to forces and is not influenced by the location or elevation.

see other post.