[Plugin: Events Manager] RSS feed not working?

hi, have you tried https://www.metalsvet.cz/akce/rss

also, for the rss per country try to modify template @ templates/templates/rss.php then do something like EM_Events::get( array('scope'=>'future', 'owner'=>false,'country'=>'US' ) )

https://wp-events-plugin.com/documentation/event-search-attributes/
to use templates: https://wp-events-plugin.com/documentation/using-template-files/

Other wordpress website widget error:

This XML document is invalid, likely due to invalid characters. XML error: Reserved XML Name at line 12, column 39

For link https://www.metalsvet.cz/akce/rss

did you added any modification to the rss template? can you post that using pastebin?