[Plugin: Events Manager] Booking removal in the front end – #_REMOVEBOOKINGFORM

that placeholder is depreciated; did you try to use my-bookings page instead? e.g. settings > pages > other pages > My bookings page

Actually I am trying to add the Cancel button on a customized page, a separate page from the “My bookings page”.

try to see templates/templates/my-bookings.php (cancel link section) then create a placeholder to use in formatting > events > Default single event format

– https://wp-events-plugin.com/tutorials/create-a-custom-placeholder-for-event-formatting/