But presumably there is also more competition for jobs using popular technologies?

Perhaps the more important metric is supply of devs relative to demand. The top paying languages, according to the Stack Overflow's 2022 survey, are generally less popular: Clojure, Erlang, F#, LISP are the top 4. While certainly not an ideal metric (e.g., perhaps salaries are skewed due to more senior devs using these languages), this hints that the demand is certainly there relative to supply as companies are willing to pony up some decent cash for these devs.