I work in software. I too had a stable job at a large Japanese firm (>20,000 employees) from 2016 until quite recently. Nice salary, good environment and no overtime. But they tried to force us back to the office without vaccines, so I started looking for a new job. I found a fully remote job at a smaller company (<2000 employees), and resigned at the start of the summer.

I've been working here for just over a month and I'm much happier. As another poster said, I did feel "lost in the machine", and a general pointlessness to my everyday efforts. Also I'd been working on the same project for many years so I did not get a depth of experience.

There are definitely positives and negatives of working in a large company vs a small company. I didn't feel like I'm harming my career at all however. Far from it, now I feel like I have more responsibility, my voice is heard, and my contributions matter more to the company, as well as having a bigger impact.