Should a FrontEnd developer learn CMS?

Question

CMS

I know HTML, CSS (SASS, etc.), JS, jQuery, some php.
Registered as a freelancer, most of the orders are related to various CMS.
Should I start learning them or move towards JS frameworks?
Will the cost of studying CMS be useful, will this knowledge be useful to me?
I want to develop in FrontEnd, but freelancing is hard to find projects focused purely on it, only if it's layout. Most of them need either turnkey websites, or layout stretching for some CMS, or plugins for these CMS.
I read one article that you need to spend at least a year learning WordPress and then specialize only in it.

Answer 1

To create themes for WordPress, subject to knowledge of HTML / CSS, it is enough to spend a couple of evenings.
And so, at least a quick look is definitely worth it.

Answer 2

I went to upwork somehow ... so there in the web category, 90 percent of orders for wordpress =\

Answer 3

FrontEnd is CMS
CMS is needed by everyone and always - this is a web front-end for filling content on the server,
you can invent your own CMS or work in a ready-made
one if 90 percent of orders for wordpress - so obviously they have burned