today I was doing some work on upgrading a client's website server. After upgrading I suddenly was thrown all of the same errors you mentioned earlier about your website.
Turns out that Wordpress does not like php8 or php8.1
The solution is to downgrade to php7
A tutorial:How to Install PHP 7.4 on Ubuntu 22.04 LTS - LinuxCapable
Learn how to install PHP 7.4 on Ubuntu 22.04 LTS Jammy Jellyfish using the command line terminal with Nginx, Apache modules examples, and support.