Hi @webmaster,
This is possible but would unfortunately require some custom coding – I would recommend getting familiar with the custom templating system within The Events Calendar by reading this guide: https://theeventscalendar.com/knowledgebase/themers-guide/
You could then use those principles to achieve this:
I’d like this additional field to display on the single event page as a button with the title ‘Photo gallery’ if a URL has been entered in the field.
I unfortunately cannot find the article or page you’re referring to that explains this in more detail 🙁
Sorry to disappoint about this last point – but best of luck with your customizations!
Sincerely,
George