On the 26. of November PHP 8.0 was launched, and since then you as a Simply.com-customer have had the option to use it on your webspace.
PHP 8.0 is a brand new version with several – and major – changes compared to earlier PHP-versions. Among other things, new functions as well as improvements to performance and security have been added.
See a complete overview of PHP 8.0 and changes here:
However, we recommend the continued use of PHP 7.4, which for the moment is our standard PHP-version, as not even WordPress 5.5 is completely compatible with PHP 8.0 yet.
Remember that you as always – at your own responsibility – can choose your preferred PHP-version for your webspace. Read more about this here: https://www.simply.com/en/support/faq/php/503/