I've been using this as funny small talk while talking to students at universities, but it's actually true: wanna be the most valued and irreplaceable employee in your corporation? Become a #Cobol developer. And you'll have a lot of time for your open source hobby projects as a bonus. https://blog.hackerrank.com/the-inevitable-return-of-cobol/
That's classic. I always took it as a bit of folklore.
But we have similar situation at the moment. We have acquired company in Kenya and they have legacy system in Clojure. And according to this https://www.thecrazyprogrammer.com/2019/07/highest-paid-programming-languages.html it is the best paid language currently out there. ;)
Generalistic and moderated instance.