Hi @exolon,
Yes, It is possible to add subscribe button on event detail page.But for this you need to do some customization in plugin.
For that first you need to override template file “content-single-event_listing.php” at your child theme side.For template override info, you can read this doc : https://wp-eventmanager.com/knowledge-base/template-files-override/
In new template file “content-single-event_listing.php” which created in your child theme side, you can create button for event subscribe here.
Thank you.
Regards,
Rita Kikani