Mandarin is weird, because I don't think it's that hard to speak at a passable level, mostly because the grammar is so simple. Many people are spooked by tones, but I think their importance for simple communication can be a little overstated.

But then, learning to read and write requires enormous additional effort. When I learned in Beijing, I'd spend a couple hours a day working on grammar/speaking/listening - and then like 6 hours a day of rote practice to get familiar with characters.

I learned it in high school and university as European and I can speak decently. China isn't that good of a place for foreigner due to difficulty of getting permanent residency/citizenship. Hong Kong is the exception but the economy is not too hot there now.

I moved to Singapore although it had nothing to do with my language skills.

Even if I was fluent in mandarin, China still wouldn't be in my shortlist of countries to move to due to low salaries in engineering, poor working conditions (996), authoritarian government, etc.