Is Ruby still worth learning in 2020?

Lots of companies are still using it, and although it's not hyped that much anymore, it is much nicer to use than JS or PHP which means dealing with legacy code is less of a headache IMHO. So it will continue to be a money machine for those who don't need to be at the bleeding edge and reinvent everything.

It's also faster than Python on a bunch of benchmarks (sorry I don't have a link). The next version will have a JIT compiler so performance will keep getting better.

There's also Elixir and Crystal which are inspired by Ruby, so the spirit lives on regardless.

What's the pro of Elixir and Crystal over Ruby?

Goodness me No. Ruby has become a sunken cost.

There are better alternatives like Golang, Rust, Elixir or even Crystal. I’m not even sure why Ruby should exist or even be used in 2020, if it is still stuck in versions 2.x.

What's wrong with versions 2.x? Or what's coming with version 3.x?

No it is being deprecated in 2020.