No you can’t make the data in the extract unreadable, but you can reduce it to a bare minimum, especially with aggregation.
When you make your extract, you can first hide fields you don’t want included in the extract, filter to exclude Records you don’t want included, and aggregate to visible dimensions to pre aggregate the data in the extract (using the default aggregation for each measure)
That way you can limit the detail that is in your extract. You can make the extract only contain the values you need to display. If you pre-aggregate the extract, be careful about using additional aggregation in your viz.
Some aggregation functions can be meaningfully repeated, known as additive aggregation functions. Sums of sums for example ; or mins of mins. But others can lead to strange or incorrect results, avg of avg in many cases