I'm just gonna add that bishonen (mei shao nian 美少年) IS a word in chinese as well, and means exactly the same as what it does in japanese. 美少年 is kanji after all, and in chinese, it's hanzi lol.
It's just that bishonen is literal. Literally means "pretty (美) boy (少年)". 美男子 (bidanshi/mei nan zi) is actually used as well, quite commonly.
Meanwhile, "male god" 男神 is figurative. Like a mini figure of speech. They're not a literal god; it's just a very common slang to refer to someone who is very skilled as something as "(something) god". It's basically like saying you have god-like skills/aptitude in something (and implied that a mass of people admire-worship the person for it). In this case, it means a guy whose looks is so godly, to the point people worship him for it. Basically a better equivalent is to say someone is a (figurative) idol. Based on the other comments, this same expression isn't used in Japanese, so in Japanese you'll only understand 男神 as its literal meaning.
美少年 would just says that dude is pretty, without all the implied meaning that it's over the top beauty like a "male god" us. It's like the difference between calling someone "handsome" and an "Adonis". Both are nice, but one has the connotation of being the top of the top.
I do think bishonen is used mostly it has gone beyond its original japanese origins, and become a slang/loan word in
english as well. While the chinese slang of "male god" has not.
@sorarinnie Following what I said above, Isekai also is kinda the same in how it has taken a slang meaning in english directly.
In chinese there's an equivalent which is basically "穿越" (to pass thru) but means basically means transmigration, and is a slang in the same effect as isekai (before isekai was even popular), but also covers time travel and reincarnation. Meanwhile, 異世界 (lit "another world") is still understandable, and can be understood literally, but might not have the same strong effect as a slang.
We're just more used to the japenese versions and they've rooted as slangs.