Do you need to create a user persona for a personal project that you are going to add on your portfolio? I ask because if you do create a user persona, it will basically be invented and assuming since there is no real client involved.
Yes. Persona development should be part of your design legwork, included as part of your research (even if you are your own client), and part of your thought process. This will help you showcase your work to potential employers as part of your portfolio, which is especially important if the analysis you did ended up somewhere, like in a series of low- or high-fidelity prototypes.
You won't regret it. And it's not as trivial as it seems, so I would also encourage you to talk to people about your ideas and see if they can identify more personas or at the very least, they will help you focus.
Personas provide a basis for design discussions by concentrating many pieces of user data into key, focused, believable descriptions of your primary audience, [which means that] product development takes those personas' needs into account.
By creating an explicit persona you make the concept of the user, concrete rather than elastic.
Do you need to create a user persona for a personal project that you are going to add on your portfolio?
I would say "yes". Because persona are useful in understanding your customer well and so ending up with a good product, whether the project is personal or not.
Wearing my interview hat seeing somebody talk about things like persona in their portfolio would be relevant and useful.
I ask because if you do create a user persona, it will basically be invented and assuming since there is no real client involved.
… not if if it will "basically be invented". Because that isn't a persona. Persona are not works of fiction. They're research based.
Because, wearing my interviewer hat, as soon as I see a persona description in a portfolio I'd be asking things like "And how do you create this? When and how did you do the research? How do you analyse it? Who did you talk to? How did you choose what to include/exclude form the persona description? etc.".
If the answer was "I made it up" then I'd be thinking "This person doesn't actually know what persona are…" and the interviewee would be in a vastly worse position than if they'd not been a persona to start with.
Generally fictional persona for fictional projects don't make particularly impressive portfolio pieces in my experience - unless the focus is mostly on the graphic design end of the UX spectrum. Because they almost never have the interesting constraints that make real projects challenging.