If the shapefile is too big (above 2GB) and I have split it into 2 shapefiles, how do I load that 2 files into ArcGIS Runtime via
ShapefileFeatureTable, or something equivalent?
You can't. You'd have to work with two separate tables.
I mean you could technically use the AddAsync method to copy features from one table over to the other, but that would just cause that table to exceed the 2gb limit of shapefiles, and defeat the purpose of splitting them in two.
Perhaps it would be better to move to Mobile Geodatabases that are more modern, a lot faster and doesn't have the same size limitation?