Thanks for your inquiry.
BMI088 doesn't accept external signal to trigger the measurements so that multiple BMI088s can be synchronized. And in theory it not possible to synchronize two IMUs by any means, because each IMU has its own internal clock and signal path. Even if they can be synchronized, the MCU also needs time to read their data one by one which will have delay between two IMUs' measurements.
So the possible solution could be increase the BMI088 ODR. For example if your MCU needs to read two IMUs' data at 100Hz, you can configure two IMUs to run at 800Hz ODR (output data rate). Therefore, whenever your MCU reads two IMUs' data they are pretty much close to each other in time which means they are almost synchronized.