PHP used by 77% of all websites, PHP 8 by 3%
w3techs.com
w3techs.com
[1] https://w3techs.com/faqThe biggest PHP users on the linked list don't even expose that they use PHP, but it is publicly known (though Facebook uses [or used] their own fork of PHP called HHVM).
I have no particular reason to doubt more than half of sites are run by PHP considering the portion of sites that are WordPress. However, I also have no particular reason to trust that 77% is an accurate proportion.
PHP probably gets a lot of extra hits in places it might not be used a whole lot. For a long time web host providers had it pre-installed by default. Plus wordpress is used a lot and they can detect that from the admin/edit page.
Also someone posted this thing a while back that does some detection like this to find out what tech is powering the website you are on:
I'm not related to them in any way and I don't know how accurate it is but it was interesting.
I bet they are undercounting a bit since the large content sites will keep their WordPress install outside of public view completely and the site is just headless.