Website not loading after WP upgrade to 6.2

Hi, after upgrading our webpage from WordPress v4 to v6.2, the webpage is not loading anymore – while I can still administer the site fine. It may be related to the theme we use (The7.2), as the page loads fine when I change the theme. But then obviously our design is gone. And there my “expertise” reaches its limits – has anyone an idea how to proceed best and fix it?

The page I need help with: [log in to see the link]