Variable substitution doesn't work in settings

I have a simple, straightforward Makefile that is located in ${workspaceFolder}/cpp/Makefile. If I use an absolute path in the JSON settings for this extension, the extension loads correctly; if I use the ${workspaceFolder} variable, or if I do not include makefile.makeDirectory or makefile.makefilePath, the extension fails.

To be more precise, this works:

{
    "makefile.makeDirectory": "/path/to/my/workspace/cpp"
}

and this works:

{
    "makefile.makefilePath": "/path/to/my/workspace/cpp/Makefile"
}

But this crashes, with the message Makefile entry point not found:

{
    "makefile.makeDirectory": "${workspaceFolder}/cpp"
}

and this crashes, with the same message:

{
    "makefile.makefilePath": "${workspaceFolder}/cpp/Makefile"
}

Likewise, if I omit both settings entirely, I also get Makefile entry point not found.

This is my first time using this extension, but I've been coding C++ and writing Makefiles for decades, and this specific Makefile has worked just fine in this project at the command-line for a long time: I was mostly trying to get this extension working to help my colleagues, and I was puzzled as to why it crashed on a simple, clean Makefile the moment I installed the extension. It took some significant Googling and guesswork to figure out how to fix this issue, and sadly, absolute paths are not portable: We can't commit absolute paths in settings.json since not all of our computers have the same directory structure, which makes this extension effectively unusable for our team.

I tested this under VSCode 1.68.1, running under Windows, with the project in WSL2 running Ubuntu 22.04, with GNU Make 4.3, and the Makefile Tools extension is v0.5.0.