Lavibunny is correct. For the singular to work you must use the indefinite articles 'a' or 'an' e.g. 'a strawberry', or 'an apple'. The only way grammatically that you can have "We eat Strawberry..." is if is describing a flavour e.g. We eat strawberry ice cream, raspberry tarts, etc. So if you ever say something like "We eat Strawberry", the response from a native english speaker will likely be "Strawberry what?"
They have to judge if you knew it was plural. It's hard to know what 'strawberrys' should be, and you have to make a choice when trying to "auto correct" spelling choices. Strawberrys has a smaller Levenshtein distance to strawberry than strawberries. By that metric it is reasonable to mark it as incorrect.