Maybe it has some more importance in Europe?
My impression was that a lot of the political parts of the encyclical seemed specifically informed by what's going on with the Italian center-right. §§86 and 125 also seem like they're directed at Lega in particular rather than at the global #populist right more generally. Popes, even post-1870 Popes, adopting Italy as their main reference point when it comes to assessing world politics is a long and proud tradition, of course. Perhaps Antonio or Battista Minola would be able to say more about this.
Yeah, "populism" is possibly even more abused as a political term in Europe than it is in America. Almost all the rhetoric against the yellow-green government back in its days was painting is as "the government of the populists".
I think Francis' point is precisely that this term has been so abused as to become meaningless.