Error php with version 8

on my site matomo plugin (wordpress) creates a lot of problems, even error 500. I had to disable it. He tells me that the php version is not correct, he would like v.8 but when I change it the site no longer works. I send you a screenshot.
Thank you

Hi @valeriosky
Sorry, I don’t understand exactly the initial and final situations…

  • What is the initial PHP version? What happens there?
  • What is the final PHP version? What happens now?