There isn’t one universal distance, because “not visible” depends on how you define visibility and on the whole imaging chain.

A practical way is to define a threshold such as the object projecting to 1 pixel (or a few pixels) on the sensor. Then the distance depends on:

• focal length
• sensor size
• image resolution
• object size
• lens sharpness/aberrations
• contrast with the background
• atmospheric conditions (haze, heat shimmer, etc.)
• viewing size and distance of the final image

In simple geometric terms, the object’s image size on the sensor gets smaller in proportion to distance, so you can calculate distance once you choose the minimum image size you’ll accept.

As a rough visual rule of thumb, a 2 m object may lose discernible shape at around 1000–3000 times its size, depending on conditions and viewing criteria. For a 2 m object, that suggests roughly 2–6 km before it becomes point-like or effectively invisible as a distinct square. Under ideal eyesight, one answer estimated about 8.4 km using the object’s 2.8 m diagonal and a 3000× rule.

So: yes, it can be calculated, but only after you define a visibility criterion such as pixel size or angular size.