Just out of curiosity, what was Karl Marx's opinion on women working... like what did he believe

He didnt focus on women or men. He focused on the working class mostly. Which includes both. If you're looking for leftist texts that dive into women amd their roles then perhaps engels would be a good read. There were also many women communists and socialists who were fighting for womens rights around the time of marx. So you have a lot to choose from.

I mean. His daughter Laura Marx published several works. So I imagine he was pro-women working.