If everyone is supposed to be gay, dividing physical education by genders doesn't make much sense. Details like that (eg. how reproduction and friendship works) may seem like nothing, but when you add them all up then the setting turns counter-productive for the message it tries to deliver; the impression of author not spending any effort on the "lore" (just like 99,99% of isekai / "skill" shit on the market) really makes the content feel like cheap homo propaganda.
I think you and others forget that Japan is not exactly LGBT friendly. It is a
HEAVY conservative country. It is not exactly as "forward" as Canada or other countries. You can call it "cheap homo propaganda" but let us not forget that this is a country that doesn't have gay marriage legal, lowest on 1st world nations for gender equality, thinks everyone needs to conform, and does like Trump.
Try to imagine being a gay woman in that type of country. Imagine having to explain in a world where you feel so left out because you are gay and feel you can't conform.
This reddit thread explains the whole situation. Also, I assumed they were gay but it turns out they are pansexual and nonbinary.
Let's not forget that sometimes they have no freedom in their creativity when it comes to their editor in not explaining the layout of the plot correctly. Do I think that they could have done it better? Of course. However, you have to understand that sometimes some manga are only given to the mangaka such as saying "you can only two volumes so make what you will."
You can say its lazy "lore" but calling it "cheap homo propaganda" feels off to say when you have to remember how the mangaka grew up in a culture that isn't too kind to the LGBT. The USA and other countries aren't the best but we are more lucky than other countries.