When I drag in a curve decorator OTL into Unity, I don't see any curve to edit.

When I draw a curve for the decorator, it's very sluggish moving the points.
What I want to do is draw or edit the default curve (if I can get it to appear)
to run along my dungeon corridors. Why isn't the default curve visible like in
the videos?

If you go to Houdini Engine > Create Curve and click in the scene in a few different spots to place down a raw Houdini curve, does the curve show up then?

There might also be driver problems. If you look at the Console (click on the very bottom of the entire Unity window), do you see any errors?

You can see by the screenshots there's a curve there I made, I can use it for curve decorator, however the default'curve decorator'
curve doesn't display.

Obj(id: 1, name: path): Invalid argument given: Tempated geo did not cook. Geo info may be out of date.
Object Path: /obj/CurveDecorator2/path
UnityEngine.Debug:LogWarning(Object)
HoudiniAssetOTL:buildCreateObjects(Boolean, HoudiniProgressBar&) (at Assets/Houdini/Scripts/HoudiniAssetOTL.cs:208)
HoudiniAsset:build(Boolean, Boolean, Boolean, Boolean, Boolean, Boolean, Boolean) (at Assets/Houdini/Scripts/HoudiniAsset.cs:1221)
HoudiniAssetOTL:build(Boolean, Boolean, Boolean, Boolean, Boolean, Boolean, Boolean) (at Assets/Houdini/Scripts/HoudiniAssetOTL.cs:123)
HoudiniAsset:OnEnable() (at Assets/Houdini/Scripts/HoudiniAsset.cs:769)

Right. I see the problem now, though I'm not sure how you got into that state. I can't reproduce it on my end.

In any case, it seems our curve decorator asset has a templated SOP in it that's causing problems for you.

I would say either get tomorrow's build of 14.0 (because I fixed the template thing) or turn on Import Templated Geos for your curve decorator asset. This is an option in the Inspector under Asset Settings > Cooking tab.