My main fandom place is unusual in having enthusiastically embraced OCs early on and has a vast number of shared OCs. It can be a bit off-putting to new people because by now the OCs are almost like a running joke and obviously its deeply weird to have occasional fics that are only about the OCs and yet have half a dozen people commenting on them and talking about them. But it does mean that they are obviously not self-inserts. Though even self-inserts done well are not actually a problem in and of themselves (I generally point to the character of Harriet Vane in the Lord Peter Wimsey novels at this point because she is such a screaming Mary Sue and yet very popular). But yeah, in general, someone needs to be really good to persuade you to be as interested in their OC as you are in a canon character and I'd be inclined to say that OCs are really only justifiable if you are writing casefic (or its canon equivalent) when they are often necessary, they are rarely necessary in romance stories (unless I suppose there is a pressing need to include parents or similar and canon doesn't provide any)