In a context like this:
The bunpo-check keeps showing me that the よ is not correct. If it's so, why, and if it's correct, does the よ make the sentence sounds feminine?
Japanese Language Stack Exchange is a question and answer site for students, teachers, and linguists wanting to discuss the finer points of the Japanese language. It only takes a minute to sign up.Sign up to join this community
よ by itself is not wrong, but the part before it is wrong. In this context, you have to say 歩きたいからです(よ).
よ as a sentence-end particle may or may not sound feminine depending on the type of the word it follows. よ does not sound feminine after です or だ. For details, see: how could a sentence end with (noun + "よ"?)
(からよ is a possible combination when よ is used as a filler particle, but this type of よ sounds rough and masculine, and doesn't go well with です/ます.)
Also note that you usually need an explanatory-の in the first sentence: どうしてドアを開けたのですか or どうしてドアを開けたんですか.