To add a new event category, navigate to your WordPress dashboard, Events, then Event Categories.
First, enter in the new event category's name, which will help classify what the type of events assigned to it.
Next, enter in the event category's slug. Events assigned to this new category will have this slug in their URL.
Assigning a parent category and writing a description is not necessary, but can be helpful.
When done, click Add New Event Category.
After creating a new event category, you need to match its styling to your existing event categories.
Navigate to Settings under Events. Then click the Category Colors tab.
Your new event category will appear as the category slug you assigned earlier.
Check No Border for Border Color, select a unique Background Color, and then choose which Text Color (black or white) makes the event category's name the most legible.
When finished, scroll to the bottom of the page and click Save Changes.