For a breakdown on each other quarter, you can check out this post in December here. As a whole in 2023, the total was CHF 132.9 billion or around $150 billion. That’s a gigantic leap from the CHF 22.3 billion in foreign currencies sold in 2022.
The reason why the SNB is doing this is to dampen the impact of imported inflation to the economy by supporting the Swiss franc. And one can argue that they have successfully done so, considering the inflation data in recent months.