I found a thread on twitter written by a Rabbi that claims to show Joseph of the old testament bible (torah) was genderfluid. She claims this interpretation is commonly held. Is this a common interpretation?

The answer to your title is “no”, but the person you’ve linked isn’t wrong. The basic problem here is that I think you've over-stated what R’ Ruttenberg is saying. Her twitter thread does not claim that Jewish texts paint Joseph as genderfluid or genderqueer. This would be a difficult position to maintain, since modern conceptions of gender like that are, well, modern, and thus one would be hard-pressed to find them in past documents. She calls it “queer/gender-bending Torah”, i.e. content in the Torah (Torah here probably referring to Jewish teaching in the broad sense, not narrowly to the text of the Torah) wherein male/female gender categories are not conformed to. It’s certainly examples of gender-bending in Jewish texts, but it’s not arguing that Joseph as depicted in Jewish texts was genderfluid because neither Joseph nor the writers of the texts she cites would’ve had any such concept.

Anyway, for the most part her citations are to fairly “standard” Jewish midrashic texts. I put “standard” in scare quotes because I’d like to talk a bit about what these texts mean. They’re in the genre of “midrash aggada”, which is midrash involving the narrative portions of the bible. Midrash in general is a genre of Jewish text (really, it’s a thing which can appear in any Jewish text, but also a genre in that some texts are just collections of midrashim) where the text of the bible is expounded on in some way. There are several types. One is a legal midrash (“midrash halakha”), where legal principles are derived from a text through homiletical principles and close readings of the text, using parallel words, deriving meaning from extraneous words and letters, etc. Then there’s narrative midrash (“midrash aggada”, or “aggadata” in Aramaic, or “hagada” in some forms of Hebrew/Aramaic) which expounds on the narrative. Sometimes is fills in narrative gaps, or explains something left vague in the text. Sometimes one character is associated with another (midrashim sometimes like to assume an absolute minimum of characters, so two completely separate characters might be made into one super-old character). Generally there’ll be something in the text that the midrash will be noticing and building on—a common word or phrase used in two places, an unusual phrase, a narrative gap, etc.

Many of these midrashim are found in collections, but sometimes midrashim are integrated into other texts (most notably the Talmud). While some midrashim are quite famous and widely known in the Jewish community (sometimes even confused with the actual biblical texts), most are quite obscure. It’s not mandatory to believe all of them, but in general saying they’re “just stories” would raise a lot of theological eyebrows in the Jewish world. Many are contradictory or fantastical, so a midrash-maximalist position is hard to maintain, but people sometimes try. It is a long-running point of controversy the extent to which Jewish law can be derived from narrative midrashim, and whether there’s a rigid distinction between midrashim.

The midrashim she cites are mostly not super well known (they’re no “Abraham working in his father’s idol-shop” or “Moses putting a coal in his mouth because an angel made him”), but they’re not particularly obscure either. A traditionally-educated Jew or a Rabbi would probably have read at least a few of these before. Midrashim in the Talmud generally get more readership. Some of what she notes is cited by the major biblical commentator Rashi, which is generally a way for a midrash that would otherwise be obscure to get widespread readership. One of the things she cites actually is famous for interesting reasons—Rachel and Leah switching fetuses^1 comes up in discussions of who Jewish law considers to be the mother of a child born to an egg donor and a surrogate—but that one would be fairly well known because it’s found (in part) in the Talmud tractate Berakhot, which is a fairly common tractate to study.

Basically, the texts she cites are part of the canon of Jewish text. The textual links she notes that make Joseph sound a feminine are things that many close readers of the bible would’ve noticed. But what she’s referencing are things that understand the character of Joseph to have somehow had feminine traits or aspects, not things that claim him to be a genderfluid character in the bible. I don’t think she’s claiming that, just noting that it’s “gender-bending”. Knowledge that Jewish tradition is happy to ascribe feminine traits to male characters might make modern genderfluid or genderqueer people happy, but those concepts are modern ones which both the bible and Jewish literature as a whole don’t have.

Exactly what the midrashic read is depends on where you read it. Targum Pseudo-Jonathan has the fetuses switching איתחלפו עובריא in Aramaic, but the Talmudic reference to the story (Berakhot 60a) says that the fetus of Dina נהפכה לבת “became a daughter”, without mention of Joseph. This sounds more like the fetus changing gender, but could be about the fetuses themselves switching. The Talmudic reference is older, but Targum Pseudo-Jonathan has the bit about Joseph being the other one. When this comes up in Jewish law usually it’s assumed to be a switch of fetuses, thus making Dina a precedent for Rachel being her biological mother but gestated by Leah.