Where I've landed on this one is that the difference is whether the characters understand the plot device (or investigate if they don't understand), not whether I understand it or whether it comports with my notion of what is possible. In Star Trek, the characters understand the unrealistic elements (warp drive, Heisenberg compensators, space communism, etc). In Lord of the Rings, they don't. In Star Wars, they understand some of the unrealistic elements (FTL travel, lightsabers, etc) but not others (everything Jedi or Jedi-adjacent).