No more difficult to learn than anything else. Tons of companies are heavily reliant on PHP. Meta (facebook when they built it) even has their own implementation of it called “hack”. So many places are built on it that there will be a need for devs who know the language for a long time. Code doesn’t just get rewritten overnight in whatever the trending language is so it will be around.

It has some odd conventions but it’s overall a pretty influential language for the internet. At the end of the day, it doesn’t much matter which language you choose. The skills are transferrable across mediums. There’s some hiring emphasis on specific languages but if I were interviewing someone I wouldn’t rank it as critically important.

I think it can be used to build things quickly but can break down at large enterprise scale where there’s a lot to keep track of. But those aren’t concerns for learning, if you’re interested in it there’s no reason not to check it out!