Hi,
Thank you for the details!
The issue is caused by a custom javascript library (mootools), which overrides the browser native window.Event object, causing it to malfunction. Usually that library is used for very old cross browser compatibility, but it is probably very outdated.
When I try to run an example code from the actual MDN web API, it triggers the error too: https://i.imgur.com/Y6rFdYx.png
The plugin also uses a single line of a code to trigger an Event, where the script stops with a fatal error triggered by the mootools Event override. Unfortunately we can’t do anything from the plugin perspective to stop this in any way, as it simply overrides the original browser native code.
If you remove that script, everything will be resolved. Updating it could work too. It originates from this directory, if it helps: wp-content/plugins/PW-Blog-Builder-For-VC/js/lightbox/mootools.js