I do not have the option to build a lens flare object

I do modding for the game Kerbal Space Program, in which I specifically add planets; the problem is that in order to add custom lens flares, I need to supposedly build a lens flare object in unity (a .unity3d file).

From other modders I've heard this setting called "build lens flare object" just shows up when right clicking the flare asset, however, in the screenshot below you can see this is not the case.

I've tried this with both the update of the unity editor in which the game was made, and the recommended version of unity, but in neither did this setting show up. As far as I could find, I am the only person with this issue. Does anybody know how to fix this/what's going on?