This is single document no sort. If you need to sort on multiple documents which score value (there are multiple inside the document) you are looking sort.
If you need each Dimensions Array sort Use Subquery expressions. As it so nested getting exact structure will be complex.
SELECT m.*,
(SELECT s.*,
(SELECT d.*
FROM s.Dimensions AS d
WHERE ....
ORDER BY d.score) AS Dimensions
FROM m.Schemas AS s
WHERE .....) AS Schemas
FROM messages m
WHERE ...;