I think its important to know that ShrinkWrap wraps meshes, it currently doesn’t use AI to fill in missing data in the model where there isn’t any. You’ll need to add the missing bits if you expect a solid volume. Otherwise you can take a shot at the FillMeshHoles option or the Inflate Vertices option. You can have gaps that will be forgiven, just not gaps a lot larger than your target edge length.
I used a SubD plane and pushed it around a little for the top, nothing accurately done (15 seconds maybe?)
I used InterpCrv and snapped around the interior open area and ran Patch (maybe sub 2 minutes for that action).
That was enough to get it to Inflate as a solid volume.
