Just an idea (take into consideration that I'm not a lawyer so I may be wrong). You can try something like a dual license: an open source one like AGPL for hobb

Just an idea (take into consideration that I'm not a lawyer so I may be wrong). You can try something like a dual license: an open source one like AGPL for hobbyists and people that want to use it in an open source project, and for companies or people that want to use it commercially should be able to buy a commercial license and use it in their closed source code/apps. Otherwise I think following the API of Processing in C is not a bad idea and I know that implementing the backend for a few operating systems implies a lot of work. You can also look into how other people fund their open source work like the implementer of the Zig programming language Andrew Kelly and the implementer of SerenityOS.