The event search from The Events Calendar does not work when Relevanssi is enabled. In regular use, it works, but if you try to access the event list directly with a search term in the URL, the search finds nothing.

One solution is to make Relevanssi index the tribe_events post type. Then you can enable Relevanssi in the event search by adding this snippet to your site:

add_action( 'pre_get_posts', function( $q ) {
    if ( isset( $q->query_vars['post_type'] ) && 'tribe_events' === $q->query_vars['post_type'] ) {
        $q->set( 'relevanssi', true );
    }
} );

This function will turn Relevanssi on in all searches for the tribe_events posts.

Another approach is not to index the tribe_events post type. Instead, you can add this filter function:

add_filter( 'relevanssi_prevent_default_request', function( $prevent, $query ) {
    if ( isset( $query->query_vars['post_type'] ) && 'tribe_events' === $query->query_vars['post_type'] ) {
        $prevent = false;
    }
    return $prevent;
}, 10, 2 );

This function will stop Relevanssi from interfering with The Events Calendar search. There’s a bug in the current version of Relevanssi (2.18.0 for Premium, 4.16.0 for free version): if you have enabled Relevanssi in admin searches, the event search won’t work. Disable Relevanssi in admin searches to make the search function.