IMUs themselves don’t store data, nor, generally, have any capacity for doing so. They’re simple sensor ICs that report values to the host. According to the specs, the Librem 5 uses a ST LSM9DS1. Note that the datasheet mentions nothing about persistent data storage. It can store 32 samples temporarily in a FIFO in RAM, but this is definitely not enough to compute a position history.
The host that reads it out might store data for calibration, but in the case of the Librem that code is open source so it should be possible to check.