Your version of the Kaleidoscope submodule might be too old.
There was a recent change in the plugin API. To use Version 2 with KALEIDOSCOPE_INIT_PLUGINS, you need to upgrade to the latest version of Kaleidoscope.
The error indicates that KALEIDOSCOPE_INIT_PLUGINS is unknown to the compiler.
Figured it out. For reference, go to file-preferences, click on the file path where it says “More preferences can be edited directly in the file [file path]”
And then go to subfolders packages, keyboardio, hardware, avr, 1.23.0, libraries, and replace kaleidoscope with the contents of the relevant github zip file.
My leader sequence doesn’t work still, but that’s probably just something I’ve done wrong. It compiles fine now.