Is this sentence natural or at least grammatically correct?

> 
> At least he is not a simp, which many people are.
> 
> 
> 

I was told that which shouldn't be used to refer to people, which seems to be confirmed by [this writingcenter](https://writingcenter.unc.edu/tips-and-tools/relative-clauses/):

| Pronoun | Stands For |
| --- | --- |
| who | people |
| whom | people |
| whose | people or things |
| that | people or things |
| which | things |