Well, on Twitter the other day, I asked, only partly tongue-in-cheek:
> Even in 2021, any new server-side web app with even a vain hope of being installed by people who are tech savvy but not modern web nerds should probably still be written in PHP. True or false?
The "false" responses cited things like "it doesn’t matter what you write it in as long as it runs cleanly in a Docker container" and "Node is widespread enough I think it goes beyond 'modern web nerd' at this point," and they might be right -- but I'm not certain they are.
So, I guess I'd suggest that maybe the answer to your first question ("why start something new with PHP in 2021") doesn't actually depend on getting an unqualified "yes" answer to your second question ("is there anything it does better"). If I was starting a project that I wanted to have installed by the kinds of people who will not use the word "deploy" instead of "install," if you take my meaning, then I'd at least seriously entertain whether it should be in PHP.
Now, for the kinds of projects I think get talked about on HN (e.g., actual paid jobs), this is more of a fair question. I appreciate Laravel and Symfony, but PHP in 2021 has traded the feeling of being a cargo cult version of Perl for the feeling of being a cargo cult version of Java. If I do write a new project in PHP, it's probably not going to be with any existing framework, because even the lightest one feels like endless mazes of "get a Request object from a RequestFactory by instantiating a dependency injection container and passing it to a RequestFactoryFactory".