I just opened up the repository as I solved the issue for the shared libraries and automatic builds for Projectm. At least for Mac and Linux. My build on Github actions works for these 2 platforms. Check the makefile as it is not generic enough. If you ammend the paths I think it will work for others too. I am still working on the Windows build. The code builds now, but needs a bit more testing.
You can build it from here: [kockie69/Visualizer: VCV Rack Visualizer based on ProjectM (github.com)](GitHub - kockie69/Visualizer: VCV Rack Visualizer based on ProjectM
A mac and linux version can be found here. removed parameter for mac ยท kockie69/Visualizer@c7bc2f7 (github.com)
Let me know if it is working for you.