Learn Farsi: علاقه‌شان به کارآفرینی از دوران کارآموزی به بعد بیشتر شد. - Their interest in entrepreneurship increased from the internship era onwards.

It acts as a two-part frame (a circumposition) wrapping around the noun phrase dowrān-e kār-āmuzi (the internship era). az means 'from' and be ba'd means 'to after' or 'onwards'. Together, they indicate that the change started at that specific time and the new state continued indefinitely.

Both kār-āfarini (entrepreneurship) and kār-āmuzi (internship) look very similar. What is the pattern here?

They are both compound nouns built from the word kār (work) plus a present verb stem and the noun-forming suffix -i. kār-āfarini uses the stem āfarin (from āfaridan, to create), so it literally means 'work-creating'. kār-āmuzi uses the stem āmuz (from āmuxtan, to learn), meaning 'work-learning'.

Why do we use the preposition be for 'in entrepreneurship' rather than dar?

This is because of the noun alāqe (interest or affection), which dictates the preposition. In Farsi, you always have an interest to something (alāqe be), never in something. At the B2 level, memorizing which prepositions pair with abstract nouns is crucial, as they rarely map directly to English.

The sentence uses bištar šod for 'increased'. Is there a more formal verb for this?

Yes, in formal writing or news, you might see (literally 'found increase'). However, using the compound (became more) is very natural and highly preferred in both spoken and standard written Farsi for expressing an increase in feelings or abstract concepts like interest.