Also, can I sell the games I make on your wonderful engine for money on Itch.io? And could I make a 3 hour plus game with GB studio? Can I change around the color pallet? Also can I make a JRPG?
Looking at the license, I think you can sell your games made in this engine.
I don't see any problem with making long game.
In GB Studio you are restricted to 4 colors but you can change them
I don't known if you can make a JRPG, I don't really known limitations of this game engine
More information you should be able to find here: https://www.gbstudio.dev/docs/