What’s a good first GUI project in C++ on Linux?

For a conventional desktop app, take a look at Qt and GTK. Both provide the pieces for building windows and user interfaces, and either can be a reasonable place to learn. Pick one and make something small rather than spending too long comparing frameworks.

A file converter is a useful project: choose an input file, select an output format, run the conversion, and show progress or errors. You can start with placeholder conversion logic, then connect a library later.

I’d begin with a console program that solves a real little problem, then add a GUI once the program’s core logic works. A music library organizer, a batch renamer, or a unit converter could all start in the terminal and grow into an app.

Keeping the file or conversion logic separate from the interface will make the GUI part less confusing. It also lets you test the useful part before dealing with buttons and windows.

If your goal is specifically to learn C++ desktop development, Qt is worth trying. Its documentation and tools give you a fairly complete path from a window to a more involved application. Your C# background may make the general idea of widgets and event handling feel familiar, even though the APIs and language details differ.

Try a simple notes app or a small task tracker. Add and remove entries, save them to a file, then load them again when the program starts. That gives you a few real features without requiring a huge design.

Dear ImGui is another option if you want to get a graphical interface on screen quickly, especially for a utility or a tool with buttons, controls, and tables. It’s less about learning the usual desktop-app look and more about building a practical interface with minimal fuss.

For a first project, make a tiny app that tracks a few values or lets you adjust settings. If your aim is a standard Linux desktop application, though, compare it with Qt or GTK before settling on it.

Don’t make toolkit performance your deciding factor for a beginner app. The discussion around speed tends to matter more for demanding rendering than for ordinary windows, forms, and menus. Choose based on the kind of app you want to build and which toolkit’s examples make sense to you.

A file browser for a small folder, a countdown timer, or a basic audio player could all teach useful GUI fundamentals. Keep the first version plain, then add one feature at a time.