It seems plausible to me that the author of _some_ software would have copyright of that software's output. For example I assume the authors of a 100% non-interactive, real-time rendered audio-visual art piece (c.f. demo scene) would own the copyright of the output (e.g. a movie file), even if someone else runs the software.

Another example would be an interactive game. Here the player / user contributes a certain creative input, but still some game developers retain the right to stream gameplay (=distribute the output of the software which uses certain copyrighted assets?).

I guess a game like Minecraft might "cross the line" to where some of the output (any elaborately voxel constructions) might plausibly be owned by the player.