I don't know many if any YIMBYs who are opposed to density. I know people who are opposed to density being seen as only apartments and condos.
The only other categories are heavy manufacturing (which is harder to argue for) and single family homes, which are not dense by definition.
I’m not sure if you’ve ever been to Portland but the predominant problem is still too much office and retail space (much of it empty) and not enough residential space; every apartment I have lived in and almost every apartment building I walk by day to day has vacant ground floor retail.