Magnesium carbonate (E504i)

No. Magnesium carbonate (E504i) is not one of the markers Open Food Facts uses to classify a food as processed or ultra-processed, so on its own it doesn't raise a product's NOVA group.

What it is

A food additive used to dissolve, dilute, disperse or otherwise physically modify a food additive or nutrient without altering its function -and without exerting any technological effect itself- in order to facilitate its handling, application or use of the food additive or nutrient.

A product that contains it can still be ultra-processed for other reasons: 5 of the 8 products here that contain magnesium carbonate (E504i) (63%) are in group 4 because of other ingredients or additives.

Function

Carrier: A food additive used to dissolve, dilute, disperse or otherwise physically modify a food additive or nutrient without altering its function -and without exerting any technological effect itself- in order to facilitate its handling, application or use of the food additive or nutrient.

Functional class definitions from the EU food additives regulation, via Open Food Facts.

More about magnesium carbonate (E504i) on Wikidata