I just dove into this the last few months working through a Udemy course on building a vampire survivors clone in Godot 4....highly recommend (here is the author talking about it https://youtu.be/Yd-sndQnWIo?si=yWU9WJ2roSVlMzDE). I was amazed by the tooling and had a blast doing it. I'm primarily a backend dev and this scratched a different itch. There appear to be some RTS courses but I can't vouch for them. I would find one that looks interesting and dive in. I typed out all the code and did the steps as he did and feel like I learned a ton. I am still looking to learn more about multiplayer in Godot 4, but I found a few YouTube videos and it doesn't look super complicated, especially if you are not concerned off the bat about cheaters. Additionally I have been following this project (Godot 4 MMO), the code is organized pretty well: https://jdungeon.org/ but very early in development