reads sizeof(iis3dwb_fifo_out_raw_t) bytes from the FIFO and stores them into buf (which is 7 bytes large). I suppose that the purpose is to read 7 bytes from the FIFO, because from the datasheet ...

Unfortunately, the iis3dwb_fifo_out_multi_raw_get function does not work correctly. Most likely it is due to sizeof(iis3dwb_fifo_out_raw_t). typedef struct { enum ...