I am trying to update a WordPress site and running into problems. The site had not been updated for a very long time.

I was able to update WordPress to 5.1.19, but that’s the newest version it will do as the host is running PHP 5.5. I went to the host and updated PHP to 8.2, but then the WordPress site breaks. I just get “This page isn’t working site name is currently unable to handle this request. HTTP ERROR 500″ (I get this both when I’m trying to view the site as a visitor and on the wp-admin login page.) If I downgrade PHP back to 5.5 everything starts working again. Any ideas on how can I fix this? Not sure if it’s relevant but it is hosted on IONOS.