Translation:We eat not only fish, but also meat.
"We don't eat just fish" and "We don't just eat fish" are exactly the same as if one was to use "not only" instead of "don't just". I put in a request to have it changed.. :/ I will admit though, "We don't eat just fish" is a strange way of saying it.
Can vlees in Dutch only refer to non-fish meat, or does this sentence just assume that the learner will understand the context of this sentence? In English the view that "meat" doesn't include fish seems a bit outdated from my perspective (excluding specific cultural & religious contexts).
What's wrong with "We not only eat fish, but also meat."? That was the structure they just wanted in the last question:
"Mijn zus koopt niet alleen een jurk, maar ook een hoed." "My sister not only buys a dress, but also a hat."
Update 6/30/2020: It's accepted here... https://forum.duolingo.com/comment/9268911/We-not-only-eat-fish-but-also-meat
If I said that, I would rearrange it slightly: "We eat not only fish, but also meat." That appears closer to the Dutch phrasing, but I also prefer it because the first clause implicitly constrains the second clause to refer to things we eat. When the "not only" precedes the verb, the second clause is wide open, and might just as easily be, "We not only eat fish but also kiss babies."