As we see there are 2 meanings of “so-called” that can be confused or misinterpreted, of which one implies falsehood and the other doesn’t.
One. to show that something or someone is commonly designated by the name or term specified.
“Western Countries belonging to the so-called Paris club”
Two. used to express one’s view that such a name or term is inappropriate.
“she could trust him more than any of her so-called friends”
Since so-called I feel is very often used to suggest that a title for something describes a meaning that isn’t necessarily accurate, what’s another term that simply expresses that something is titled something without judgment of the title?
The problem here, linguistically, is that any phrase which means this will take on the meaning of falsehood automatically, over time. It’s the same way that any respectable word that means “has a disability” eventually comes to be an insult and then a slur.
If you want to say something like that, the word “putative” is still pretty unfettered by negative connotations, but only because few people use it. If it were in common use, it would follow the same path as “so-called”. A more reliable approach in the long-term is to say what you mean using more words instead of fewer:
She could trust him more than any of her friends; although she wasn’t sure those people were really her friends, it remained to be seen.
It’s actually the length and awkwardness of the sentence structure that makes it resistant to misinterpretation.