The logic behind the save icon in versions KeyShot Studio 2025.2 and prior.
When rendering a large resolution, you might notice that once the image has finished rendering, there is no save icon to save the image to a file.
That you would see at lower resolutions
Prerequisites
- KeyShot Studio 2025.2 and older
Explanation
As of the version 2025.2 and older, the save icon is hidden whenever the render output is show at a lower resolution than the rendered image. This is to prevent saving a lower resolution image.
Rendering the same resolution when the output is not scaled will allow saving the image to a file.
This scaling is due to the Render output window hitting a memory limit.
When expanding the Show Image Styles panel, it will also show a waring whenever it is scaled. However the Preferences mentioned in the warning are referencing an old tab that no longer exists since restructuring the Preference options. 
It is referring to the Render output window memory limit that can be found in the Interface Tab of the Preferences.
Increasing the memory limit to 1024 should allow you to save 8K resolutions, 4096 would allow saving 15k resolutions.
Please make sure that your system has sufficient free RAM, as increasing the limit can slow the system down significantly if the available RAM is already close to capacity.