The word "work" used as a noun has different meanings. You can use it in the plural as a countable noun, i.e. "Shakespeare's works" (many different plays). But when you use it without the "s", as an uncountable noun, it can take a more general meaning (i.e. "I love the work of Shakespeare") or even refer to the combined sum of Shakespeare's creative produt over his career.

Yes, in academic writing, "related work". Collective. Only as below, when you want to stress that there was more than one output, do you use "works". . Not sure how you would use "in some work" or "in some works". In some of the related work, [2,5,7] we see an inappropriately small sample size. . In some works of the late composer, JSB, the .... was superb.