Martin, it is a fixed expression ‘ sous forme de qqc ‘, translated in context of the text as ‘ in the shape of….’
With fixed expressions it is usually best to accept the expression as it is, as a whole unit, rather than try to translate or break it into individual words.
Nonetheless, as with many prepositions, ‘ sous ‘ has an array of different meanings, and is part of a number of expressions and compound nouns.
https://www.wordreference.com/fren/sous%20forme%20de
https://www.wordreference.com/fren/sous
https://www.larousse.fr/dictionnaires/francais/sous/73753#locution
