On Linux, the idea is that you’ll escape to shell and run the Makefile yourself … or, better yet, use CMake - as that is basically the best possible way to do things on Linux.
I’ve found that ChatGPT can convert .jucer files to CMakeLists.txt projects pretty well these days, so don’t be afraid to do that.
Essentially, Projucer is great to get started - on Windows and MacOS - but once you’ve got some wind in your sails and want to build for Linux, its just generally better to have converted your project to CMake, as its really the secret sauce for cross-platform, multi-target JUCE projects …