Your manager is responsible for your performance at work. Therefore, it's in their best interest to help you resolve anything that is negatively affecting your work performance, even if it's something non-tactical.
If you are having a deeper issue (e.g. you have imposter syndrome), this is something you should talk with your manager about. You shouldn't expect them to act as a full psychologist, but they should at least be receptive of your problem and lend an understanding ear.
Venting and complaining are very natural and can act as a therapeutic exercise. Don't be afraid to do this with your manager once you have a good enough relationship.
This gets easier over time. Once you start being honest and more transparent in your manager meetings, the trust between you two increases, making it smoother to continue being open in the future.