having the USE_MAXON_API being defined - actually using C4D=true in projectdefinition.txt - is required in order to be sure that all the cinema.framework classes are properly compiled. Although there could be situations where some cinema.framework classes can work without that define, we highly discourage this approach since you can end up in situations where the code compiles until you include that specific class which indeed needs that define (which it's already happening in that case).

If specifying C4D=true actually brings too much pain, please open a new thread and let's proactively discuss the issues your code is facing and let's get rid of them.

Best, Riccardo

porting pre-R20 plugins to R20 definitively requires to review the code and deliver the changes needed to make it nicely work with the new API structure and syntax.
I warmly suggest to run through all of them and fix accordingly to what stated on the Plugin Migration section of the Cinema API C++ documentation.

Last but not least, consider that a few of the issue might be due to code-style strictness level: in such case you can consider to lower the code-style strictness (see style-check) for an initial transition and concentrate on design issues.

Best, Riccardo

it seems like you're attempting to create hybrid plugins mixing classic API with new API. Could you please check that C4D=true is actually used in your projectdefinition.txt as reported in the Project Tool section of the C++ API docs?

Best, Riccardo