For sensor fusion with the realsense’s IMU, we used the robot_localization package along with the nav2 stack. The config file can be found in src/merger/config/ekf.yaml and uses the realsense and odom topic for the motor controllers as seen below. If there are additional sensors (such as using the lidar as a odom source) you can read the robot_localization docs as linked before to add a new source.
odom0: /odom
odom0_config: [ false, false, false,
false, false, false,
true, true, false,
false, false, true,
false, false, false ]
# realsense imu..
imu0: /camera/camera/imu/sample
imu0_config: [ false, false, false, # ignore position
true, true, true, # use orientation
true, true, true ] # use angular velocity