When copying a Nintex Form, Sharegate displays the following warning:
This form (...) references functions that are not available at the destination: Function1, Function2. The form will be copied but it will not behave as expected until it is updated.
Some functions available in Nintex Forms may not be available when the source and destination SharePoint environments do not have the same version. Sharegate gives this warning when it encounters unsupported functions in order to explicitly state which functions are used in the form and must be changed manually.
At the destination, edit the Nintex Form and change all references to the specified function(s). The warning message will contain the control and/or parameter which contains the function and requires a manual input.