Hi @alexliii,
Thanks for reaching out. What version of PHP you use is specific to users and their own environment. While PHP 8 can provide performance improvements, there may be some aspects of WordPress or third party plugins that don’t fully support PHP 8 and higher. This doesn’t necessarily mean anything will break. You may just notice some warnings or depreciation notices if checking your sites PHP logs or WordPress debug logs. Information on WordPress core support for PHP8 and above can be found here.
Depending on your hosting plan you may easily be able to switch between PHP 7.4 and 8 or higher, which can be useful for testing. You can use a plugin such as Site Kit or use PageSpeed Insights directly to compare performance after switching between both.
Hopefully the above is of use. As this query isn’t specific to the Performance Lab plugin I’ll close this support topic. If you’re looking for further information on PHP with WordPress you can also use the Fixing WordPress forums.