The standard maximum function is supported, generating MAX (expression) and returning a value of type matching the type of the expression. When dragging a Maximum into a variable, the following tree element is created.
Columns and/or other non-aggregate expressions can be moved over the (empty) branch of the tree.
The option to compute the maximum over distinct values only is provided, resulting in the generation of MAX(DISTINCT expression). This option is enabled through the Properties panel. Double-click on Maximum, or highlight it and click Properties.