That said though, the version of PHP you are talking about was written 23 years ago. The language has changed a tremendous amount over 23 years. The state of the tool 23 years ago would be a very poor reason to choose or avoid it today.
Hell, Java is roughly the same age as PHP. Nobody in their right mind would dream of using that first version of Java today. It isn't that the tool itself is bad. Rather, the tool has improved dramatically over the last two decades.
Also applies to JavaScript, and to be fair, many other scripting languages. None of them were perfect in v.1 and to add missing features it was often necessary to bend them in ways that are inconsistent with the rest of the language.
No language/tech stack is going to ensure success, or have no challenges. But learning from the past is not a weakness.
What's the lesson you are learning from?
The lesson I see is that any language, even PHP, will give you success if you "build something people want".
I read lots of startup "shutdown" stories - and I've not read one that mentioned the choice of "PHP" (or any language) as the reason for shutting down.
So if your comfortable with PHP - punch out what you need to get started...
Is it suitable for EVERY application? No. But then again, nothing is a one-size-fits-all solution for all problems.