Is this sentence correct? Grammarly does not take it a mistake.
There you can see how much the scores will change.
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"Is the below sentence correct?" <-- below cannot be used as an adjective.
(you want to say: "Is the sentence below correct?")
As for the statement: "There you can see how much the scores will change."
Yes! If you factor out that 'much' implies the 'rate of change (of the scores)' and since change is uncountable, 'much' is expected here.
Personally, I wouldn't use 'will' (considering it is a modal that serves others functions which are probably not relevant in the statement) but instead say, "are likely to" or "are expected to" or simple "are to" (change).
Further to Alex StJohn's and Alberto Solano's answers:
If we refer to the amount by which a score changes, we would say e.g. "The score will change by 10 points". The word "by" is needed. Therefore, if the OP's sentence refers to the amount of change, it needs the word "by". It should be one of the following: