I am also curious on how much did those hackers stole and what's their purpose on donating some amount on random charities?
Well, it is not actually stated how much but based on the article the OP has provided, these Darkside hackers had extorted millions of dollars from companies and it is also said that now they wanted to make this world a better place that is why they posted these two receipts of $10K worth of Bitcoin to two charities.