As I said, I'm not wading into controversial debates.
All I'll say on that is that the Avari vanish from Middle-earth's history after the opening pages of "The Silmarillion" concerning the awakening of the Quendi at Cuivienen and that the chief distinctions Tolkien were focused on, in that tale, were linguistic first and foremost and then geographic: who stayed and who didn't stay. I couldn't find a single reference to appearances in those passages, and I read them very closely as presented in the tale of the published text, which again, is my "gold standard" above any drafts and letters.
As far as I'm concerned, the status of Third Age Avari living in climates completely altered by multiple cataclysmic changes in the history of Arda is entirely up to the reader's imagination, especially in a Third Age context. Tolkien's mind and heart were set in the northwest of Middle-earth, in Beleriand chiefly, and then in Numenor, Lindon, Eriador, Rhovanion, and Gondor, with all else sketched out in only the barest of details (*with only the places Frodo and Sam experience from Minas Morgul onward as the chief exceptions).
Another thing to keep in mind is that the frame narrative matters. "The Hobbit" has two versions - both written by Bilbo, one a lie to cover-up the Ring and the other with the truth behind the Ring included. LOTR has Frodo and Sam writing it - with Merry and Pippin lending input - and then it gets copied by Fingedil King's scholar in Gondor in FoA 172 during the reign of Eldarion. "The Silmarillion" is a collection of various writings held by Elrond in Rivendell, translated by Bilbo into Westron, and the other drafts are various writings as well.
So, how could Fingedil King's Scholar, or Elrond, or any of the Hobbits, know what happened to the Avari or what they looked like? They couldn't. They never went out there.
Now, it's also true that they never saw a Death Star plop atop Mordor (*that's where . . . . I'd take issue. Please, no wars between star destroyers and Great Eagles, amusing as it sounds, tyvm!). My way of interpreting is this: the published text gives some details, and then I'm free to take those details, start with then, and then imagine them as I will.
Honestly, it's what makes Tolkien's body of work great: that the contradictions, while troublesome for ending a story as I mentioned above, also mean he succeeded in his original vision: to mimic the patterns of writing mythology. What happened to Iphigenia, daughter of Agamemnon? Well, Aeschylus will give you one answer, Euripides will give the opposite, and then you get to decide which ending you like best. That's part of how it works
Cheers!