I'm in a situation many probably recognize in that the existing codebase has quite a few areas where it can be improved (lack of testing, overly complex architecture, a hard-on for static classes and methods everywhere, no monitoring).

Unfortunately I see myself as a rather average developer on a code-level and would like to improve my programming and designing skills. I've read the book A Philosophy of Software Design and enjoyed it thoroughly but so far it's the only resource that I found that touches on this specific area of software development.

I use Youtube channels like Nick Chapsas (recommendations welcome) to stay aware of new developments in the C# world and inspiration of replacing bulky implementations with cleaner ones.

What other tools or resources can I use to autonomously improve my designing skills in order to make maintainable software?