actually I'm a little bit off when I double-checked my memory: it's every 2016 blocks, not precisely every 2 weeks. So if nobody mines the next 2,016 blocks, it could take much longer than 2 weeks for the difficulty to be adjusted downwards.
But once 2,016 blocks are eventually mined, then the difficulty will be adjusted downwards, and the amount it is adjusted downward is exactly proportional to how long those last 2,016 blocks took to mine.
Apparently in July 2021 blocks took 20-120 minutes to mine instead of 10, after China cracked down on mining. Once those 2,016 blocks went through though, the difficulty dropped by 28%.
