"in which" and "during which"

Is "in which" interchangeable with "during which"? I've seen them replaced with each other in videos and articles. But no books explain the question.

Not always.

in often means within some kind of boundary, but during means within some time frame.

For example "the jar in which I hid your money", or "the country or region in which he spent his childhood". These phrases cannot work with "during which".

As for things which take time, like meetings or weeks, there is sometimes a difference:

• "the week during which I was sick" could mean I was sick for seven days

• "the week in which I was sick" could be, I was sick for maybe one day, but I am talking about the whole week surrounding that illness.

But for telic actions (that is, things which happen at once and don't take a long time) that happen inside of a length of time, "in" and "during" can often both work:

• The business meeting in which he embarrassed himself or the business meeting during which ...

• The holiday during which I met her or the holiday on which ...

Then there are phrases where you simply need to learn which is the fitting preposition. Usually in that case it will be in. For example:

• I did it in a grand/selfish/loving manner. The manner in which I did it was ...

• I looked the monster directly in his third eye. The eye in which I looked him ...