When people say there’s been an “𝑥 fold increase in such and such.” They mean such and such is 𝑥 times as big.
If you get something that actually folds like a sheet of paper, the amount of layers doubles each time. One fold = twice as many layers. Two folds = four times as many layers…
It’s a separate meaning of fold. Fifth definition for Merriam Webster.
fold
5 of 5 suffix 1 : multiplied by (a specified number) : times —in adjectives a sixfold increase and adverbs repay you tenfold 2 : having (so many) parts threefold aspect of the problem