The most important fact about Java Minecraft that most people are missing is that long after Notch left the company they started distributing deobfuscation maps for it:

C:\Users\Username\AppData\Roaming\.minecraft\versions\1.17.1\1.17.1.json

Look for: client_mappings & server_mappings

https://launcher.mojang.com/v1/objects/e4d540e0cba05a6097e88...

https://launcher.mojang.com/v1/objects/f6cae1c5c1255f68ba483...

The tricky part is they don't provide deobfuscation tools, so everyone makes their own and it's a mess.

But Minecraft is for all practical purposes open-source since 2018!

Legally you cannot distribute the deobfuscated binaries, so most people map the code.

I would probably use the 1.17.1 as the last "open" minecraft and start a fork that you compile and work with after deobfuscation and then re-obfuscate at each release.

Dunno what the legal team at Microsoft would think about that!