From Xojo Documentation

Property (As String )
aListColumn.MinWidthExpression = newStringValue
StringValue = aListColumn.MinWidthExpression

Supported for all project types and targets.

The minimum width of the column as a string expression that can include spaces and the percent sign.


The following line sets the minimum width of the first column in a ListBox to 15% of the total width of the ListBox.

Listbox1.Column(0).MinWidthExpression = "15%"