Is there any passage in the Torah which says that we as Jews should not talk a lot about our religion and ourselves to the goyim ?
Thank you for your question.
There is such an idea, however it isn’t part of the written torah, in the sense that it isn’t it is clearly written in a specific verse, rather there is such an idea written in the oral torah, and it is alluded to in a one of the verses. The idea is that the Hashem and the Jews consider the giving of the Torah on Mount Sinai to be a tremendous gift, and a show of love from Hashem to the Jews. Therefore we specifically do not want to teach the oral Torah to non-Jews, and it is considered part of this private intimate relationship, between Hashem and the Jews. In Deutronomy 33-4, tit is written that Moshe told us the commandments of the Torah, which is “Morasha” (lit. inheritance) to the Nation of Jacob. In the oral torah, we are told that the word “Morasha” should also be read “Meorasa” which would mean “betrothed to”. Meaning that the Torah is to be kept as a wife, to build a relationship together, and not to be shared with anyone else aside from those that are part of this relationship. Therefore, we do not teach Torah to non-Jews.
It is important to mention that any gentile that wants to join the Jewish people, will take it seriously and perform the mitzvos, can join the Jewish people and convert.