According to the general recommendations, one should tell real
weaknesses, but they are not related to that type of role and do not
affect my work. For instance, some recommendations are to say that you
are a little bit shy but this could affect how you communicate the
results and do not ask the questions you should ask.
Unfortunately this is one of those "it depends" questions that's hard to answer without knowing the interviewer and the workplace.
Sometimes (quite often?) the interviewer doesn't have much experience or training in interviewing, and has no idea why they're asking this kind of question beyond "we're supposed to ask questions and this is the kind of question other people ask in interviews". If they don't really know why they're asking, some kind of non-answer might be fine.
But a more experienced interviewer will usually have some purpose behind their questions. If I were asking this kind of question, it'd be in order to gauge whether the candidate is able to assess their own strengths and weaknesses, and whether they have enough confidence to be open about them. (It's very hard working with people who are more concerned with saving face than with asking for help when they need it.) Having seen their CV and written application, I might already have ideas about their possible weak spots, but it's important to me to know whether they understand what matters to the job.
If I got a non-answer, I would probably be redirecting the focus: "okay, what do you see as the biggest weakness relevant to this job?" (Or better yet, making that the question in the first place.) If you were to answer "shyness", I might well think that you didn't really understand what the job is about.
FWIW, last time I applied for a job, I got a similar question: "what would your greatest development needs be in order to be successful in this job?" I was aware of two things that were likely to be major strikes against me: I didn't have experience in that particular field (so I'd need to acquire a lot of domain knowledge) and I was applying for a promotion without having had acting experience working at that level before (main reason for missing out on a similar job a few months earlier).
I talked about those, and even with those acknowledged weaknesses I got the job ahead of at least two other qualified candidates, so I guess honesty was a good approach for those interviewers!
Often you won't know whether you're interviewing with the kind of people who appreciate openness or the ones who want you to bluff. But you can at least ask yourself which kind of people you'd rather get a job with!