After upgrading PHP 7 to PHP 8 the frontend appears to be broken. The front end comes with the error "mb_strlen(): Argument #1 ($string) must be of type string, array given". This appears to be a core issue.

The temporary solution is to disable caching. 

The credits are for Github: see php8 issue mb_strlen() for more information.

Error message 'mb_strlen(): Argument #1 ($string) must be of type string, array given'

The error message mb_strlen(): Argument #1 ($string) must be of type string, array given

Disable caching

Go to Global Configuration -> System -> System Cache and set it off. Click [Save & Close] to save the settings.

Website shows fine.

And the website shows fine.