Depends on where you are right now, I learned elm during the second year of my career and so far it has proved its worth by providing good opportunities and great learning.
It is also a good place to start a career in fp languages.
But if you are already experienced in front end development then it's less clear how learning elm can help your job chances. You already should have ample opportunities then.
This is a slightly odd take, technologies can gain rapid growth at any stage. Take python for instance it was a niche language for a majority of its lifespan but then it suddenly got crazy popular.
Unfortunately FP jobs seem to be niche and extremely location dependent. Python and Javascript are winning the market, FP had a slight increase in interest but sadly fading, job wise anyway.
I say this as someone who didn’t know much FP 8 years ago, invested a bunch of time learning, picked up a few good jobs using it but now cannot get hired due to no FP specific work in AU and non FP roles seeing 8 years of FP get a bit weary, despite a decade of Java, Python, PHP etc before my FP roles.
ELM is a great Trojan horse into learning FP if you want to learn FP though.