Hmm. Npgsql supports polygons in some sense, but you have to add some custom bits on top I suppose? I'm not sure how querying works though.
SQLAlchemy is pretty much the only framework I've seen do this pretty well, though I have plenty of other qualms with it. Still probably my favorite ORM overall.
and no support for spatial data types. it's why i'm still mostly using SQLAlchemy and Python - i'm a big fan of .NET Core, though.