Jailbroken 3DS scene is usually for modding the console OS itself given how easy it is to run custom firmware. And for ports, and emulation. While the GBA has a pretty dedicated community for custom games and romhacks, people often create games for the platform at gamejams because of how great the dev tooling is. It's a bit lackluster on the 3DS, but I did find the Love Brew[0] framework to be really nice. Even has simulator support[1] for testing your builds locally, though fonts will look much different on real hardware, with likely a bunch of other gotchas. Running out of RAM being a big one.
[1] https://github.com/lovebrew/nest
edit: compared it to the GBA homebrew scene since it's a large dedicated community to derive pros and cons between the two from. Switch is still receiving updates from Nintendo to brick your system.