I agree that Duolingo should also accept "I will eat a potato without sausage." That sentence is more natural to a native speaker than the "correct" answer.

Duolingo should also accept "I will eat a potato without sausage."

Я хочу їсти картоплею з грибом!

"a potato" is a much better translation

The article 'a' is not implied nor necessary at any part of this sentence and should be accepted with or without it