Good afternoon Scott and welcome back!
Thank you for reaching out to us.
We are sorry to hear about the fact that you are unable to customize the Events Calendar. Yikes!
I would love to help you with this topic.
It is totally possible that your theme is not compatible with our built-in customizer.
In any case, as a first troubleshooting step, could you please provide us with your complete system information in a private reply using the instructions found in the following link?
https://theeventscalendar.com/knowledgebase/sharing-sys-info/
Secondly, could you tell me if your site is part of a multisite network ?
Best regards,
Geoff B.