Hey, guys. I've been playing minecraft for the last 12 years. And I'm a software developer. I've seen vídeos of people coding stuff for mods, but I have no idea where to start. Is there a Java lib I need to install? What's the project structure? Do you used maven or gradle for this kind of project? I'd love to contribute to some open source mod project. My research online is not taking me anywhere, I'd like someone to show me around. Thank you!
You have a couple of different options for mod loaders. Forge and Fabric are the big ones. Forge is the most popular, but development documentation is scarce for certain things and they tend to not be very beginner friendly. Both of these require Gradle, but Gradle is generally already provided and does not require installing.
For Forge, you'll have to download the Forge Mdk (Minecraft-development-kit) and read the README.txt file that comes with it for setup instructions. Or this for the AIO instructions (you'll be required to download Mdk anyway, but that guide will give you everything you need.)
For Fabric, read this for setup instructions, and this for basic development tutorials.
Many other different mod loaders exist, but you'll have to search for them yourself.