Finding a problem is easy. Finding an easy problem that you can solve is hard. For example, many folks might (or used to) think that building out a simple GUI

Finding a problem is easy. Finding an easy problem that you can solve is hard. For example, many folks might (or used to) think that building out a simple GUI with 3 buttons in C++ was easy (until they saw the code and didn't understand most of it compared to building an integer loop that adds 2 numbers). IMO, go for something simple like advanced math functions. The basics almost always exist in most languages, so try out something like a rate calculator, etc.