The parameter shows the default value of the WorkingFolder parameter.

But at runtime, the parameter is used.

Normally if you add a reader FME will automatically add a parameter for the source file(s), this can then be used to parameterize your input.

If you want to keep one part of the path in a different parameter you may want to consider creating a private one (Workingfolder) and referencing that in the Source dataset parameter, like this:

First I create the private parameter, then added the reader which came with the automatically generated parameter SourceDataset_CSV2, pointing to the full path of the csv file used to create the reader. Then I edited that parameter to use my Workingfolder parameter and added the wildcard.

Dear redgeographics, dear erik_jan,

Many thanks for your help!

Even if the parameter is replaced in the editor, it is well used on runtime.