The phrase "possibly a very stupid question" is typically used to acknowledge that a question may seem silly or obvious, but the person asking it is unsure of the answer and genuinely seeking clarification.
People may say this phrase as a way to preface a question that they fear may be perceived as foolish. It is also a way to acknowledge that the question may have an obvious answer, but the person still needs clarification.
No, there is no such thing as a "stupid" question. Asking questions is an important part of learning and gaining knowledge. What may seem like a silly question to one person may be a genuine inquiry for someone else.
Remember that there is no such thing as a "stupid" question. Everyone has different levels of knowledge and understanding, and asking questions is a way to learn and grow. Also, try to create a safe and non-judgmental environment when others ask questions, so you will feel more comfortable doing the same.
Instead of using that phrase, you could simply ask the question without any preface. You could also say something like, "I'm not sure if this is a silly question, but can you clarify...?" This acknowledges that you may not know the answer and are seeking clarification without labeling the question as "stupid."