Yes, that's my understanding. So for example, "lärare" is both a singular and a plural noun. I'm no expert, but this seems like one of the few times when an "en" word has the identical singular and plural forms.
My Finlandssvensk husband often looks sideways at Duolingo, and this is one of those times. You don't say Finlandsk or Finländare, you say finsk or finar. And you never use words like ingendera...it's a bit dated, like your greatgrandma is teaching you Swedish.
A finländare is someone from Finland regardless of their mother tongue. A finne is someone from Finland whose mother tongue is Finnish. And ingendera is a common word in written Swedish which you will definitely encounter if you ever want to e.g. read books and newspapers.