"I do not see this ice cream."
Translation:Nie widzę tych lodów.
Not really. Ice cream is usually plural, although it's possible to use singular "lód" for one ice cream on a stick (lód na patyku), or an ice cream cone (lód w waflu/rożku, rożek lodowy, etc.).
The first meaning of "lód" is simple "ice", not an ice cream. But if you were to interpret it as a singular ice cream, it'd be "loda" (one of the many examples when a masculine word is grammatically treated as animate for no reason). In your sentence, which is perfectly grammatical, you don't see ice.
Because when a direct object uses an accusative case in positive statements in Polish, it turns into a genitive case in negations:
- „Widzę (kogo? co? accusative) lody.”
- „Nie widzę (kogo? czego? genitive) lodów.”