I think one could make xantham gum as a processed culinary ingredient (Nova group 2) ingredient, so long as it isn’t packaged with preservatives.
The bill itself calls out using USDA databases for various ingredients and various sections of federal regulations, so I can't comment too much about how they'd feel about xanthum gum without diving deep. Not to go off on a tangent, but just from the bill's text, I can say for sure they don't like nonnutritive sweeteners, which I think really hurts diabetics choices at reducing their reliance on insulin while still enjoying nice treats. Although not too important for a school meal, it's definitely part of the ultra processed conversation and why it's not a simple thing to categorize food into groups.
For reference: xanthan gum specifically would fall afoul of the rules, as... a (ii) stabilizer or thickener, (iv) coloring or coloring adjunct, and (v) emulsifier.
https://www.hfpappexternal.fda.gov/scripts/fdcc/index.cfm?se...
It's quite silly that it's classified as a coloring agent and an emulsifier, when it's neither of those things.