I think it all depends on the region. But also realize if something is popular, it also means that you have tons of competition that are probably cheaper than you.

What I do is I learn the mainstream enough to know what it is all about and to pass a HR selection. The moment that I need to apply for the job I already have a head start and can focus to learn it fast prior for the interview.

The key in becoming a good developer is that you can adapt fast. never that you excel in one framework or language. Learn to make your brain placid enough to quickly to unlearn things and relearn something new in a week or a month. C++ took me a month to get used to the rest normally one week or so.

I definitely agree with the other poster. Try to get the general gist of what's going on frontend. However for backend I'd recommend something like python's framework Flask. It's very easy to get into. thenewboston even has some intro tutorials on youtube that are great. Django is a good pick aswell. Most any framework is wanted in the job market so you should be good. It's more about being able to learn and pick up what they want you to.