How to add custom search e.g. taxonomy?

Hm, that would depend on how you would like it done, and how many events is “a large number”. One unfortunate limitation of the Eventbrite API is that paging is fixed at 50 events, so we have to handle that while also handling paging for the WordPress page, which will get messy quickly if you want to add another layer of filtering on top of that.

Our best suggestion would be to make templates that bring back the events you need directly from Eventbrite, rather than filtering from the default full (but paginated) set. You can work with the search endpoint and any of its params: https://www.eventbrite.ca/developer/v3/endpoints/events/

Hope this helps; just open a new thread if you’re still having issues.