In my opinion, by the time you've passed some threshold for understanding such systems, either direct coding experience (jobs or Open Source) or reading good corporate engineering blogs are the only things that will build on that knowledge.
Here are the corporate engineering blogs which I've found to contain the most interesting projects:
Discord: https://blog.discordapp.com/tagged/engineering
Dropbox: https://dropbox.tech/
Facebook: https://code.fb.com/
Instagram: https://instagram-engineering.com/
LinkedIn: https://engineering.linkedin.com/blog
Netflix: https://medium.com/netflix-techblog
Pinterest: https://medium.com/@Pinterest_Engineering
Twitch: https://blog.twitch.tv/en/en/tags/work--twitch/
Twitter: https://blog.twitter.com/engineering/en_us.html
Twitter: https://blog.twitter.com/engineering/en_us.html
Uber: https://eng.uber.com/