What causes fear of the unknown?

Lack of predictability
Feeling that you don’t have enough information to make accurate predictions can cause your anxiety to rise. One way to counteract the lack of predictability is to get more information.

For example, if you’re experiencing fear of the unknown related to a new school or neighborhood, you might consider exploring the area before your move. You can make in-person or online scouting expeditions to find out more about what your new life will be like.

Lack of control
Feeling that you can’t control your circumstances is sure to cause your anxiety level to rise. Age and disability can both decrease your sense of agency.

To reclaim your sense of agency, you can start by analyzing your circumstances and listing the things you can and cannot control. You can decrease uncertainty by making a plan that includes steps you can take in areas within your control.

Fear of the Unknown: Causes, Symptoms, Risk Factors, & Treatment (healthline.com)