Yet it shows up on radar, infrared, cameras, and with the naked eye? And people repeatedly claim to see it perfectly clearly? The evidence is only shabby on film because whenever they get a clear picture on film, it becomes immediately clear that it's not a UFO.
Please explain to me why there are so many videos of supposed UFOs making mundane everyday flight movements, but video suddenly becomes impossible whenever it makes one of these "non-human" flight movements that humans claim to see with their naked eye just fine?
What does "another dimension" mean to you? There is no physical meaning to this suggestion, nothing that suggests there are "other dimensions" for beings to live in where they would be separate from this one. It's an idea from scifi writers who don't know physics, not a real component of any physical theory. While other dimensions have been hypothesized, they would be a part of this reality that you're in too, not separate from it, and anything existed in our reality would be in all those dimensions equally because they're tied together in one experience, not something you can move between.
Imagine someone saying they existed in length and width dimensions, but not the height dimension. It's nonsensical, NOTHING in physical reality works that way. You can't exist in 2 dimensions and not exist in the 3rd. In the same way, even if there are 10 spatial dimensions (which is highly unlikely), we would be existing in all of them simultaneously, not in one or the other.
There easily could be life more advanced than us. There's just zero evidence whatsoever that it's anywhere within a thousand light years of us.