Changes introduced with Cinema 4D R21 make it necessary to recompile C++ plugins.
The MSVC settings of the R21 SDK enable support for Advanced Vector Extensions (AVX) by default. Clients, that do not support this instruction set, cannot load the created plugin binaries.
The AVX settings are defined in the frameworks\settings\Base.props file. To disable AVX support, simply remove the line
On macOS, it is advised to enable the legacy build system when using Xcode 10.1+. The legacy build system is enabled under “File” / “Project Settings” / “Section Shared Project Settings/Build System” / “Legacy Build System”.