It’s an easy trick: they just check the domains of the email addresses of people who created an account and display the logos of the high profile ones.
Writing Solid Code by Steve Maguire - 245 pages but really well written and an enjoyable read. Examples in C but principles are applicable with any language.
I've been there! I definitely felt the same 4-5 years ago after 15 years as a software developer. I then changed to a support engineer position on a product for software developers (i.e. Travis CI). And it was amazing! All I was doing all day was troubleshooting/debugging customer issues. Given my background as a dev, I could dive into the codebase when needed and also look at the logs and metrics to understand what was happening. I also had the chance to code some tools to help deliver a better support experience (e.g. Slack bots, admin dashboard). This is definitely my new calling and I'm currently looking for a new position on a similar product after a rewarding 4+ years at Travis. Hope this helps!