Question: I was studing how to say school subjects in mandarin and I saw this sentence:

我最喜欢的科目**有**艺术，中文和化学
(My favorite school subjects are art, chinese and chemistry)

Why the use of 有 in this sentecence?

Could I say/write: 我最喜欢的科目是**是**艺术，中文和体育

Answer: 
Both are ok.

Why the use of 有 in this sentecence? Because here the "科目" in "我最喜欢的科目" is kinda list, so we can say "我最喜欢的科目有艺术，中文和化学", there are Art, Chinese etc in the list. "有" is the same meaning of "there are"
Both should be fine, it might be easier to think about those ones as some sort of a colon symbol(its basically what it does in this context).

a colon symbol referencing this site <https://grammar.yourdictionary.com/punctuation/grammar-colon-usage.html>

"Use a colon to introduce an item or list, if the list comes after a complete sentence or independent clause..."