Tagging onto @teascade's #gamedev resources list, here's some engine-y stuff I found and still find to be helpful:

Robert Nystrom, "Game Programming Patterns": http://gameprogrammingpatterns.com/. Some of this will be familiar but other parts of it might be more novel, e.g. framerate-independent simulation and entity systems.

For entity system architecture reference, I like browsing through the links at http://entity-systems.wikidot.com/es-tutorials. I have so far enjoyed using and modifying https://github.com/alecthomas/entityx.

Alexander Overvoorde's https://open.gl. My OpenGL experience more or less stopped in the fixed-function era, and I found this to be a great help in getting up to speed. I also find Anton Gerdelan's OpenGL tutorials (http://antongerdelan.net/opengl/) very useful.

I have been told many, many times that Raph Koster's Theory Of Fun For Game Design (https://www.amazon.com/Theory-Game-Design-Raph-Koster/dp/1449363210) is excellent. One of these days I will read it.