Learn what brings value to you and your professional career. Whether that is C#, Java, PHP, or in this case RoR. The ship has not sailed at all. Take a look at their last conference and at their last achievements. This could be a very good moment to get into it, even more if you can use it at your current workplace. Don't just sit down waiting for an answer without context on the internet. Just do it.

I have finite time and energy, if I put that time on RoR i can't put it in Golang or Python etc .. Thus my question

Far more legacy code out there than green fields projects. All of that RoR code represents a lot of opportunity. And companies still write new code with Rails. Rails heavily influenced other frameworks such as Laravel and Django so concepts transfer.

I have learned many languages and tools in my career, many of which I only used for a short time. I don't regret learning any of them.