As of Robot Framework 3.2, an argument with a default value can be represented as a ('name', 'default') tuple. Doing so allows Robot Framework to do automatic argument type conversion before passing argument values to a remote keyword.

From https://robotframework.org/robotframework/7.1.1/RobotFrameworkUserGuide.html#getting-keyword-arguments

As explained in the above table, default values can be specified with argument names either as a string like 'name=default' or as a tuple like ('name', 'default'). The main problem with the former syntax is that all default values are considered strings whereas the latter syntax allows using all objects like ('inteter', 1) or ('boolean', True). When using other objects than strings, Robot Framework can do automatic argument conversion based on them.