Honestly I wouldn’t even call doctor who science fantasy. It’s just pure fantasy set around space travel and aliens. There’s absolutely nothing science about it, and they really don’t even try to make it seem that way. Anything that should have some sort of science explanation is just hand waved away, and thus internally inconsistent. The dr who universe is basically full of magic. Magic potions, magic wands, magic enemies, magic travel boxes, magic immortality, etc.

I think the sonic screwdriver is about as close as they have ever come to trying to explain any of it, and they basically only did that to point out the (rather absurd, story-necessary) limitations of the thing. One still has no actual idea what it can do or how it can work, just what it usually does and what it can’t do (sometimes and/or probably).