I found switching software taught me the most. Every software teaches you something different and even if you return to the software you were using - it gives you a better understanding of what is available and new things to discover. It refreshes your thinking because you could learn something new in each different game development software.
There's free software like Godot and then a lot of paid software have free versions or trial versions with some examples and tutorials that teach you the software, for example, GameMaker and Clickteam Fusion, so you don't have to spend money.
However, on the Unity side - I completed the Junior Programmer pathway from Unity Learn- it gave me a good insight into what the software has to offer and even though a lot of it was not what I was interested in, it helped me to learn the basics of programming in Unity and gave me some fresh ideas Junior Programmer - Unity Learn
I also enjoyed this one: Real-time Animated Storytelling - Unity Learn - it gave me insight into a section of Unity I wouldn't have discovered on my own. It helped me to think of my games in a different way - many of my games have a story element - but this would allow me to animate the story, not just show the text on screen - it's something extra that I can do.