I'm always stuck in this B-movie trope that ETs are shape shifting gaseous-gelatinous blobs. But really until confirmation noboby knows or they ain't talking.

Also, don't know about the nano-bot trope of sci-fi stories as an alternative to other bio-sentient style lifeforms, apparently we are considered bio-stuff.

Then again differently enabled realities may be all around us, dimensionaly or literally, micro or macro even as close as the nose on our faces. We merely lack the methodology to sense ETs or we are stuck in what is defined as the space-time manifold construct.