"IN 1/2 MS MATRIX"
This recording mode lets you record with mid-side (m/s) mic signals through inputs 1/2. The sub menu simply lets you adjust the relative levels of mid channel and side channel. Here is a short intro to m/s:
mid signal represents the sounds that "sound" the same in both left and right side (L + R), and the
side signal represent the sounds that are different in each side (L - R).
One way to record the side signal is with a figure-8 mic angled 90 degrees from the mid (omni) mic. The mid signal is simply recorded by positioning the mic as usual towards the source.
Source and additional info on M/S: https://www.uaudio.com/blog/mid-side-mic-recording/
"L/R MS-RAW MONITOR"
This area let you choose how to listen to m/s recorded material.
STEREO will combine the mid and side channel into a normal L/R stereo mix, making it suitable for easy monitoring using headphones and conventional setups.
RAW puts the mid channel in left side and the side channel in right side. This is not a very convenient way of monitoring, since most activity will be in the mid channel, and you then get an unbalanced mix. However you may haw an M/S dedicated monitor chain for which this is suitable (which you most likely don't have since you're asking about this stuff :-D)
Source, manual page 85-87: The Manual