I fondly remember building toy apps earlier in my career. Like Twitter clients, simple CLI tools, etc.
What's a fun (relatively simple) toy project that you think might be useful? In my day-to-day life/work I don't have that many simple problems that need solving, so having some constraints should be ideal.
To keep the project relatively simple, you could start by focusing on the core functionality of inputting and tracking income and expenses. You could then add additional features as you become more comfortable with the project and have more time to work on it.
Another idea could be building a simple task or to-do list manager. This could involve creating a program that allows a user to add, edit, and delete tasks, and also mark tasks as complete. The program could also have features such as categorizing tasks, setting due dates, and generating reminders for upcoming tasks.
As with the budgeting tool, you could start by focusing on the core functionality of adding and managing tasks, and then add additional features as you become more comfortable with the project.
I hope these ideas give you some inspiration for your toy project!
They all have slightly different export formats, and it would be neat to have cleaned up transaction data.