Why does BMI088 have 4 interrupt pins?
The two pins dont have to do the same thing. The datasheet shows there are two types of interrupts supported on this chip. A new data interrupt (page 18) and a fifo interrupt (page 19) for both the gyro and accelerometer. The datasheet explains the difference of the two but I dont really understand the fifo interrupt.

Also, usually with ICs that have configurable pin functions you'll see the same pin function on multiple pins. Depending on how you lay out your board it may be convenient to have that function on one pin vs the other based on where that signal routes. To have that signal be able to originate from multiple places gives you options.

On page 22 it says that the interrupt pins (on this page specifically 3 and 4) can be configured as inputs and will no longer act as interrupt pins. i.e they act as just general input pins.

Link to the product page (scroll down to documents for the datasheet) :
https://www.bosch-sensortec.com/products/motion-sensors/imus/bmi088.html
Edit: had multiple English mistakes