I don't think most people are well versed, or even aware, about when a human embryo becomes a fetus unless they are biologists, fertility doctors, ob-gyns or have dealt with the issue personally and directly by TTC, being pregnant and/or having miscarriages - or having a partner or someone else close to them who has done so.

The impression I get is that most posters here have not had these personal experiences (yet).

It's true that human gonads don't clearly differentiate until 6-8 weeks.

But it's not necessarily true that until that point there's no observable/observed sex differences in M & F human zygotes or embryos.

It's long been customarily assumed that sex differentiation in humans and other mammals begins with gonadal development and the hormone differences that result - and that all the rest of the sex differences in humans follow from, and are the result of, developing different gonads & sex hormones. But research into genes and stem cells in recent decades has shown this not to be the case.

https://onlinelibrary.wiley.com/doi/full/10.1002/jnr.23884

"Robust sex differences" have been found in the progenitors of placenta cells of M & F human zygotes as early as 5 days post fertilization. (The placenta usually forms at day 6/7 after fertilization.)

The placenta is required for the growth and survival of the fetus during pregnancy, and facilitates the exchange of gases, nutrients, waste products, and hormones between maternal and fetal circulation. The placenta is formed 6–7 days postconception, and is composed of specialized epithelial cells called trophoblasts [1]. Trophoblasts are one of the earliest lineage differentiation events of the mammalian embryo, arising from the outer extraembryonic trophectoderm cells of the preimplantation blastocyst. During implantation, trophoblasts invade the maternal epithelium and differentiate into two types of specialized progenitor cells [2]. Syncytiotrophoblasts (SYNs) are multinucleated terminally differentiated cells that synthesize hormones for sustaining pregnancy. Cytotrophoblasts are mononucleated undifferentiated progenitors that can differentiate into SYNs and extravillous invasive trophoblasts (EVTs), which anchor the placenta to the uterus. These early differentiation events are essential for placental formation, as impairments with trophoblast cells result in miscarriage, pre-eclampsia, and intrauterine growth restriction.

Fetal sex influences in utero development in healthy and complicated pregnancies, where male fetuses have increased risk of peri- and postnatal mortality, and females are smaller during gestation [61–63]. Because predisposition to many adult diseases that are sexually dimorphic (including type 2 diabetes, depression, and coronary heart disease) originate during this period [64], it is important to understand the origin of these sex differences. A number of reports profiled the placental transcriptome using full-term placentas and found sex differences [65–67], yet there are no studies examining the initial stages of trophoblast formation, which occurs early during the first trimester. Here, we used an in vitro differentiation model system, where hESCs are converted to trophoblastic cells using BMP4/A/P culture conditions, to identify sex-specific expression profiles for the progenitor cells of human placental trophoblasts.

We found that there are robust sex differences in hESCs, the differentiation pathway of hESCs to trophoblastic progenitors, and in differentiation day 5 trophoblastic progenitors.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6916123/

https://www.liebertpub.com/doi/abs/10.1089/scd.2018.0081

https://onlinelibrary.wiley.com/doi/abs/10.1002/bies.201800073