Modded installations suggest the default .minecraft directory path even though it hasn't changed

Clicking on "click here" will only set the Game Directory field to the default .minecraft folder path. (i.e. C:\Users\<username>\AppData\Roaming\.minecraft on Windows)

This makes no sense, as the instance is already using the default directory anyway, as indicated by "<Use default directory>"

If you already have a path set, click the button and it should suggest that you use the .minecraft game directory.