How to Display Multi-Option for large quantity of options

I am creating a web application that requires a user to select from 400+ options. This is absolutely mandatory as it is for B2B software.

I want to break it up into categories. However, there may be close to 30 categories with 25-50 options in each category. This creates a long drop-down but cuts down on the number of options available to the user.

I am looking for advice, critique or possible examples of how others have handled this sort of issue.