Dude, it’s all BL but with different age ratings.
“Shounen ai” and “Yaoi” is a western (old) thing if you like to use I respect you, but using one to belittle other is stupid.
Generalizante all R18 BL as bad just because they show sex is a kinda homophobic you know ? Is sex in straight tv shows/ books/mangas ok but not lgbtq+ sex? I don’t know if you think this or you’re aware of it, but it’s important to pay attention on it, Also, 1/1000 of the mangas published in Japan are translated for you to say every Yaoi plot is based on sex. I don’t know how old are you but do you fell uncomfortable with R18 scenes? Ok, don’t read. But don’t spread misinformation and don’t such a dumb generalization.
This is a good article to read by the way
Futekiya is an official site based in Tokyo to read mangas in English and some Articles in their blog ( I recommend if you can, buy licensed works to help the author ^^)
https://futekiya.com/bl-vs-yaoi-vs-shounen-ai/
Why did this got labeled as a Yaoi ;-; I don't want any thirsty Fujoshis to come here and sexualize my boys whole completely missing the point of the story