To date I've studied the following, but don't have the free time to build anything of significance:
- Web Application Security
- 97 Things Every Software Architect Should Know (book)
- Modularization / Single Responsibility / Programming Best Practices
- A little bit of React
- Test-Driven Development
- Some administration related info in my bread-and-butter of choice (Java)
- Project Management
- A variety of books on leadership
- Technical leadership
In security and architecture I'm definitely on the beginning side of things and may do more.
I'm wondering: is there much else out there topic-wise that could provide any value?
The answers to those questions determine what you need to study if you're going to stay within a company. Don't study React to study React. Study React because you want your project to utilize it (or to move to a project which already does). It has zero value for study beyond that purpose if you're going to stay in place and not using it (and assuming you're not just studying it for personal edification or to feed into some other learning goals; I'm learning Go not for work, per se, but to practice more with distributed/concurrent applications which is for work, but will likely be done in another language or languages). If you're in a position for it, start a pilot project utilizing it. If not, find an amenable and like-minded manager who can put you in a position for that pilot project. And failing that, study leadership/management (find a mentor) so you can get into a position to push a pilot project through.
generally a great resource for mid/seniors.