I mentioned this in Message 4 above, but I know they also use that ValueTypeEnum in other situations also. Below are all of the Links I found where it is being used within the 2026 online API help documentation.
All these are Attribute related: Attribute.ValueType Property , AttributeSet.Add Method , & AttributeSet.AddAttributes Method
These are Content Center table column related, and they do use the Boolean one: ContentTableColumn.DataType Property & ContentTableColumns.Add Method
These are MiniToobar related, but do not include the Boolean one, just Double & Integer: MiniToolbarSlider.ValueType Property & MiniToolbarControls.AddSlider Method
So, the Boolean variation is being used by the ContentTableColumn, but apparently not by Attributes or that MiniToolbar control. And I know that the ByteArray variation is being used by the Attributes system, for storing internal iLogic rules and iLogic Form specs within the Document.
In Message 6 above, I mentioned that this would be a good 'idea' to post in the Inventor Ideas board, and so I just did a quick search in that area, and since I did not find one, I just made one myself. I will post the Link to that Inventor Idea post below, so that it is easy for every one to find, and vote for, so that we can hopefully get this ability either fixed, or added sooner.
https://forums.autodesk.com/t5/inventor-ideas/attribute-valuetype-allow-enable-kbooleantype-valuetyp...
Wesley Crihfield

(Not an Autodesk Employee)