Steps to reproduce:

Actual results: "Variable" row is empty - clicking it opens nothing - so no variable type can be chosen and the entry cannot be given a value

Expected results: The Variable row offers the variable types

Reproducible with versions: 6000.7.0b2

Can’t test with versions: 6000.6.3f1 (the Smart Strings option does not exist)

Tested on (OS): macOS 26.5

Notes:

The documentation only ever shows the scripting route - "Add variables in script with the Add method", with C# examples - and never describes filling a group in the Inspector. Either the Inspector should support it, or the list should not present "+" and an editable Name as though it does
The deprecated Variables Group shows the Variable field correctly
The row renders correctly once the managed reference is not null, which narrows this to the type picker alone. Setting one entry's variable from script to an "ObjectVariable" makes that entry display as a foldout with the concrete type's own fields, and that "Value" field then behaves normally - the object picker opens and the reference can be changed to any other object. The untouched entries in the same list keep an empty "Variable" row. So everything about the Inspector works except choosing the type in the first place