You can feel like an impostor in a role you invented yourself.

Even the role you built yourself can feel borrowed. There is nobody who appointed you, no qualification that certifies it, and the sense of being found out arrives anyway, because the feeling is about visibility rather than about legitimacy. Inventing the position removes the external authority but not the internal question.

When it comes, note that the feeling is not evidence and that it does not track competence. Ask what specifically you cannot yet do, since that is the answerable version. Everything else in the feeling is about being looked at.