As someone who looked at CVs and portfolios of candidates: I got the best impression from projects that were completed. One small, but working and finished thing beats many half-finished grandiose projects.
For concrete ideas, first of all I think it's best when you create something that is useful to you. Be it a todo list app or something that fetches discounts from a webshop you regularly use. Don't be afraid to steal ideas from others. It's perfectly fine to look up the topic you want to work on and find inspiration.
Some more concrete ideas:
I have some ideas in mind but I guess the most difficult part is where to start.
Thinking about getting a Raspberry Pi as I have seen some really interesting projects out there! :D
I suggest following tutorials and customizing them with your own ideas. This seems like a set of nice beginner tutorials: codeclubprojects.org/en-GB/python/ (I linked that not really knowing your knowledge level, so I tried to link something that's super easy).
Also, since you specifically mentioned building a portfolio, I suggest learning how to use Github so you can have a place to publish your projects. Good luck!
Raspberry Pi Foundation seems to have a wide variety of great projects in various languages which is quite convenient.
I have started experimenting with Github by publishing small projects and stuff, but still so much to learn about this platform!
We're a place where coders share, stay up-to-date and grow their careers.
We strive for transparency and don't collect excess data.