Is there a word for when, say, in an artwork, there are various items that are completely different to each other, or anachronistic? Like, for example, a watch from the 1800s and a Snoopy figurine?
Formally, you could talk about them being an "incongruous" juxtaposition. And informally, you can say that they are "like chalk and cheese".
For the example of the watch and Snoopy, I would say the items are unrelated, if I saw them, for example, on a shop shelf.
Maybe you are looking for "surrealist", which is an adjective describing anything that was incongruously juxtaposed.
"Surrealism" refers to a movement which specialised in fantasy and incongruous juxtaposition.