A word to represent 'non-friend' relationship

In Chinese, there's a word to explain a state of relationship, '路人' originally means people on road, when something happened, '路人' is kinda character that won't join the trouble itself, but watching it.

But now, '路人' has a meaning of 'not friend', you may know him, or he know about you, but you won't have deep relationship, they just walk by your life, but not close to you. is there an English word to represent it?

looks like it's not 'acquaintance' because they may be stranger of each other.

some example of '路人'

侯门一入深如海，从此萧郎是路人。

After entering the aristocratic mansion, it was deep as sea, the one true love is _____(passerby?).

description: she can no longer find love because she became a slave.

他就是个路人，我都不认识他。

he's just a ____(randomer?), I don't know him.

description: someone is trying to clarify the relationship

路人局别太认真了。

don't be too serious when playing with ____(random teammates?).

description: game matching system sometimes gives you bad player.

为什么很多人分手后都成了路人?

why many people choose to be like ____(stranger?) after breaking up?

description: they choose to forget each other instead of continuing to be friends.

一堆不明真相的路人在那瞎起哄。

A bunch of _____(bystanders?) who doesn’t know the truth are squatting there.

description: a little bit derogatory.

Two words that are most like your '路人' translation are "bystander" or "onlooker", but they may not be suitable in the sense that you want. If not, there is "neighbor" which is often used to mean neither an enemy or a friend. It can mean someone merely nearby. As others have suggested, I do want to recommend "acquaintance" as the best choice to use. It is probably the most common usage in English.

https://www.thefreedictionary.com/bystander

https://www.thefreedictionary.com/onlooker

https://www.thefreedictionary.com/neighbor

https://www.thefreedictionary.com/acquaintance

An interesting word to add to your vocabulary is the word passerby, which means

A person who passes by, especially casually or by chance.

The word is not used frequently in the US, but it encapsulates quite nicely the elements of chance, transitoriness, and emotional distance.