PHP 7 is the minimum system requirement for Joomla! 4 website every server will have to comply with sooner rather than later.
Is My Hosting Ready?
At the moment of writing, every hosting provider should have been ready for transition. PHP 7 isn’t a new thing. It has been around for over two years. If you’re not sure what is the PHP version your site is running at, fret not. Go to Joomla! Backend of your website and navigate to System -> System Information then click on PHP Information tab. There you can see what is the PHP version your site is running at:
If first number is anything other than 7, then your server is not ready for Joomla! 4.
In that case, contact your hosting provider immediately.
What About JomSocial?
In almost decade long history, we tried to keep up with latest Joomla! standards and web technologies as soon as they were becoming available. That said, JomSocial offered immediate support for PHP 7 back in February 2016 (PHP 7 was released in December 2015.) and ever since then all subsequent releases of JomSocial were supporting PHP 7.