Are you sure you’re using 2.21.3 in grasshopper? I suspect you’re actually using some 3.x version (which, won’t be compatible with Speckle.Core)
The namespaces you’re showing (e.g. Objects.Structural, Objects.GIS, etc..) only exist in the 2.x.x versions of Speckle.Objects, where all objects are namespaced Objects.
In the 3.x.x versions of Speckle.Objects, all object models are namespaced under Speckle.Objects., and many of the namespaces you’re showing no longer exist since we’ve switched to a DataObject based design.
(see this topic for discussion on this change)
You should either use 2.21 everywhere, and reference everything via using Objects. namespaces etc…, and enjoy all of the v2 object models.
OR
Remove your reference to Speckle.Core, and reference only v3 of Speckle.Objects, referencing everything via using Speckle.Objects. namespaces, where you will find a much leaner set of object models to match the data sent from our next gen (i.e. v3) connectors.