shouldn't művészek be accepted as an answer, as 'female artists' is not specified?
It is now.
Still not being accepted for some reason.
"Ők művészek vagy pincérek?" is accepted. You might have made a mistake or come up with some other solution which isn't added yet.
Where is it written that the artists or the waiters are female?
Nowhere and they don't have to. Művész and pincér are accepted.
if művésznők, why not pincérnők? one would asume the speaker sees the gender.
Hm. Good question. Anyway pincérnők is now accepted.
I think pincérnők shouldn't actually be accepted, since the english is "waiters", not "waitresses".
Yes, artists don't have specified gender, but waiters are male, so I think the correct translation would be "művészek vagy pincérek"
Isn't "waiter" gender neutral?
yes it can be, but in older usage it referred to males and waitress referred to females. Currently waiter is gender neutral; sometimes the word server is used, also gender neutral
pincérnők is not in the Duolingo dictionary. Is this an oversight or does the word not actually exist in the Hungarian language?
It does exist and I'm not sure how seriously the Duolingo dictionary should be taken.
Please help me understand why I would not use the "van" term in this sentence: "Művészek vagy pincérek vannak?"
It's because the third person "van" or "vannak" can (and must) be omitted in this type of sentence. In this case, it is good to add "Ők" to the front to make this more formal, but I don't think it is strictly necessary.
I just got burned with "Ők művészek vagy pincérek vannak?" 23-április-2020
As AndyDuoHungarian's comment explains it right over your comment - you got burned rightfully. No "vannak" in this type of sentences.
If you're going to write the date format in Hungarian, it's 2020. április 23.
van is singular - vannak is plural