grammar - some of his most characteristic work or some of his most characteristic works?

I am a Korean English teacher. I am teaching about Monet.
But I have encountered a grammatically strange expression like the following first sentence.
https://www.telegraph.co.uk/news/uknews/1551703/Cataracts-the-key-to-Monets-blurry-style.html
Monet suffered from cataracts for much of his later life.
During that time, he produced some of his most characteristic work.

During that time, he produced some of his most characteristic works.

I think that in the sentence, the word “work” must be changed into “works.”
Am I wrong or is the original incorrect?
Could you please explain which is correct or incorrect?