The Projucer itself is not meant to be an IDE, it’s more a project management tool with a code editor
As you usually use JUCE to build applications for various systems from the same project sources, you create an appropriate exporter for the each target system and the Projucer will create a Project that you can open in that IDE and build your application trough that IDE.
For Linux you have 3 options with JUCE 5:
- Makefile. You can build your project from the command line this way but it differs from the other exporters as it doesn’t target any IDE. Only recommended if you primarily develop on a different platform and just need a quick solution to build your project under linux
- CLion. This is my preferred way, as CLion is a really well working & powerful IDE. Downside: You have to pay for it
- Code::Blocks. This is an IDE but not comparable to any modern IDE. I’d see this as a fallback solution in case you don’t want to pay for CLion
With JUCE 6 there will be a full CMake support. This means you should still be able to use CLion but also any other IDE that uses CMake as its project file format. Not sure which other options there are, probably VSCode could be an option here.
So if you are just getting started and want an easy start I’d recommend you to download a free trial of CLion so that you can focus on learning to code JUCE applications first without needing to worry about building too much. After your trial period expired, you could decide to stick to it or figure out what other solutions there are. Especially with Linux there are a lot of different options.
And if you still wonder what that build feature inside the Projucer means: This is for the Live Build engine, which is an optional Projucer Plugin. However, using these extended features is something I wouldn’t recommend to you as a beginner