I’m not part of the support team here…
I see you are using Theme Dejavu… I have not experience with that theme..
least I tell you directly..
.. looking at your website it is a “Content Sidebar” Widget..
<div id=”text-3″ class=”widget widget_text”>
Events Manager displays information just like Posts and Pages.
The “sidebar” you are looking at is in a “Post”.
Generally… Posts don’t always have full screen option.. while Pages often do.
This might be overstating the obvious….
Go into your normal Admin of the site… Go to Widgets Page… look for Content Side Bar.
Try this also.. I believe its the Theme developer..
https://mysitemyway.com/docs/Sidebar
So in a nutshell this is a Theme issue.
So when you set up Events Manager.
Settings –>
–> Pages
First option is…
Display events as “Posts” in the drop down box.
If you set up Events Manager as “Posts”
ask the Theme developer how to remove that “sidebar” from Posts.
If you set up Events Manager as “Pages” then obviously you would direct your question about Pages –> sidebar.