Problem after update to 6.4.8

Have a look at
https://wordpress.org/support/topic/update-from-today-crashed-my-site/

There is described how to fix this issue.
I copied it here

TO FIX THIS IS EASY:

This is a typo in class-theme-my-login.php file the variable should be $query not $wp_query….

open file: theme-my-login/includes/class-theme-my-login.php
go to line 264…

edit:
// Bail if not the main query
if ( ! $wp_query->is_main_query() )
return;

change to:

// Bail if not the main query
if ( ! $query->is_main_query() )
return;

Ralf